#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/rope>

#define ll long long
#define pb push_back
#define f first
#define s second
#define sz(x) (int)(x).size()
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define ios ios_base::sync_with_stdio(false);cin.tie(NULL)
#define ld long double
#define li __int128

using namespace std;
using namespace __gnu_pbds;
using namespace __gnu_cxx;

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
template<class T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>; ///find_by_order(),order_of_key()
template<int D, typename T>struct vec : public vector<vec<D - 1, T>> {template<typename... Args>vec(int n = 0, Args... args) : vector<vec<D - 1, T>>(n, vec<D - 1, T>(args...)) {}};
template<typename T>struct vec<1, T> : public vector<T> {vec(int n = 0, T val = T()) : vector<T>(n, val) {}};
template<class T1,class T2> ostream& operator<<(ostream& os, const pair<T1,T2>& a) { os << '{' << a.f << ", " << a.s << '}'; return os; }
template<class T> ostream& operator<<(ostream& os, const vector<T>& a){os << '{';for(int i=0;i<sz(a);i++){if(i>0&&i<sz(a))os << ", ";os << a[i];}os<<'}';return os;}
template<class T> ostream& operator<<(ostream& os, const deque<T>& a){os << '{';for(int i=0;i<sz(a);i++){if(i>0&&i<sz(a))os << ", ";os << a[i];}os<<'}';return os;}
template<class T> ostream& operator<<(ostream& os, const set<T>& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T> ostream& operator<<(ostream& os, const set<T,greater<T> >& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T> ostream& operator<<(ostream& os, const multiset<T>& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T> ostream& operator<<(ostream& os, const multiset<T,greater<T> >& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T1,class T2> ostream& operator<<(ostream& os, const map<T1,T2>& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
int ri(){int x;scanf("%i",&x);return x;}
void rd(int&x){scanf("%i",&x);}
void rd(long long&x){scanf("%lld",&x);}
void rd(double&x){scanf("%lf",&x);}
void rd(long double&x){scanf("%Lf",&x);}
void rd(string&x){cin>>x;}
void rd(char*x){scanf("%s",x);}
template<typename T1,typename T2>void rd(pair<T1,T2>&x){rd(x.first);rd(x.second);}
template<typename T>void rd(vector<T>&x){for(T&p:x)rd(p);}
template<typename C,typename...T>void rd(C&a,T&...args){rd(a);rd(args...);}
//istream& operator>>(istream& is,__int128& a){string s;is>>s;a=0;int i=0;bool neg=false;if(s[0]=='-')neg=true,i++;for(;i<s.size();i++)a=a*10+s[i]-'0';if(neg)a*=-1;return is;}
//ostream& operator<<(ostream& os,__int128 a){bool neg=false;if(a<0)neg=true,a*=-1;ll high=(a/(__int128)1e18);ll low=(a-(__int128)1e18*high);string res;if(neg)res+='-';if(high>0){res+=to_string(high);string temp=to_string(low);res+=string(18-temp.size(),'0');res+=temp;}else res+=to_string(low);os<<res;return os;}

const int N=2505;
int dp[N][2*N];
void test(){
	int n=ri(),m=ri();
	string h;
	string d;
	rd(h,d);
	int c2=0;
	for(auto p:h){
		if(p=='B')c2++;
	}
	for(auto p:d)if(p=='B')c2++;
	reverse(all(d));
	for(int i=0;i<=c2;i++){
		dp[0][i]=dp[1][i]=0;
	}
	for(int i=2;i<=m+1;i++){
		char my=d[i-2];
		for(int j=0;j<=c2;j++){
			if(my=='W'){ //dud
				dp[i][j]=dp[i-1][j]+1;
				if(j)
					dp[i][j]=min(dp[i][j],dp[i-2][j-1]);
			}
			if(my=='Q'){ //1
				dp[i][j]=max(1,dp[i-1][j]);
				if(j)
					dp[i][j]=min(dp[i][j],max(0,dp[i-2][j-1]-1));
			}
			if(my=='B'){ //2
				dp[i][j]=dp[i-1][min(m+1,j+1)]+1;
				if(j)
					dp[i][j]=min(dp[i][j],dp[i-2][j]);
			}
		}
	}
	for(int k=sz(h);k<=sz(h)+sz(d);k++){
		vector<int> cnt(3);
		for(auto p:h){
			if(p=='B')cnt[2]++;
			if(p=='Q')cnt[1]++;
		}
		int hs=sz(h);
		int dind=sz(d)-1;
		while(hs!=k){
			if(cnt[1]==0&&cnt[2]==0){
				break;
			}
			if(dind==-1)break;
			if(cnt[2]){
				cnt[2]--;
				hs--;
				if(dind!=-1){
					if(d[dind]=='B')cnt[2]++;
					if(d[dind]=='Q')cnt[1]++;
					dind--;
					hs++;
				}
				if(dind!=-1){
					if(d[dind]=='B')cnt[2]++;
					if(d[dind]=='Q')cnt[1]++;
					dind--;
					hs++;
				}
			}
			else{
				cnt[1]--;
				hs--;
				if(dind!=-1){
					if(d[dind]=='B')cnt[2]++;
					if(d[dind]=='Q')cnt[1]++;
					dind--;	
					hs++;
				}
			}
		}
		if(hs!=k)continue;
		//printf("%i: %i %i\n",k,cnt[1],cnt[2]);
		if(cnt[1]>=dp[dind+2][cnt[2]]){
			printf("%i\n",k);
			return;
		}
	}
	printf("IMPOSSIBLE\n");
}
int main()
{
	int t=ri();
	while(t--){
		test();
	}
	return 0;
}