#include<bits/stdc++.h>
#define fi first
#define se second
#define mkp make_pair
#define pii pair<int,int>
#define ll long long
using namespace std;
const int maxn=2e5+100;
string s0,s;
int main() {
	ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);	
	int T;cin>>T;
	while (T--) {
		int n,m,k;
		cin>>n>>m;
		cin>>s0>>s;
		for (k=n;k<=n+m;k++) {
			int c1=0,c2=0,j=0,nk=n;
			for (int i=0;i<s0.size();i++) c1+=(s0[i]=='Q'),c2+=(s0[i]=='B');
			for (;nk<k&&j<s.size();) {
				if (c2) {
					c2--;nk++;
					c1+=(s[j]=='Q'),c2+=(s[j]=='B');j++;if (j==s.size()) break;
					c1+=(s[j]=='Q'),c2+=(s[j]=='B');j++;if (j==s.size()) break;
					continue;
				}
				if (c1) {
					c1--;
					c1+=(s[j]=='Q'),c2+=(s[j]=='B');j++;if (j==s.size()) break;
					continue;
				}
				break;
			}
			//cout<<k<<" "<<j<<endl;
			if (j!=s.size()&&c1==0&&c2==0) {
				cout<<"IMPOSSIBLE\n";
				break;
			}
			if (nk!=k) {
				cout<<k<<endl;
				break;
			}
			for (;j<s.size();) {
			//	cout<<j<<" "<<c1<<" "<<c2<<endl;
				if (j+1<s.size()&&c2&&s[j+1]=='W') {
					c2--;
					c1+=(s[j]=='Q'),c2+=(s[j]=='B');j++;if (j==s.size()) break;
					j++;if (j==s.size()) break;
					continue;
				}
				if (c1) {
					c1--;
					c1+=(s[j]=='Q'),c2+=(s[j]=='B');j++;if (j==s.size()) break;
					continue;
				}
				if (c2) {
					c2--;
					c1+=(s[j]=='Q'),c2+=(s[j]=='B');j++;if (j==s.size()) break;
					j++;if (j==s.size()) break;
					continue;
				}
				break;
			}
			if (j==s.size()) {
				cout<<k<<endl;
				break;
			}
		}
		if (k==n+m+1) {
			cout<<"IMPOSSIBLE\n";
		}
	}
}
/*
2
4 6
1 1 8
7 2 5
1 1 7
3 2 6
8 1200000
100000 1 100000
100000 1 12345
100000 2 100000
100000 2 12345
100000 1 100000
100000 1 12345
100000 2 100000
100000 2 12345


*/