#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return true; } return false; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return true; } return false; }
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define mp make_pair
#define si(x) int(x.size())
const int mod=998244353,MAX=2505,INF=1<<30;

#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")


bool mada[MAX][MAX+MAX];
int dp[MAX][MAX+MAX];
int sumA[MAX],sumB[MAX],sumC[MAX];

int main(){
    
    std::ifstream in("text.txt");
    std::cin.rdbuf(in.rdbuf());
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    int Q;cin>>Q;
    while(Q--){
        int N,M;cin>>N>>M;
        string S,T;cin>>S>>T;
        T+='.';
        
        sumA[0]=sumB[0]=sumC[0]=0;
        for(char c:S){
            if(c=='Q') sumA[0]++;
            if(c=='B') sumB[0]++;
            if(c=='W') sumC[0]++;
        }
        
        for(int i=1;i<=M;i++){
            sumA[i]=sumA[i-1];
            sumB[i]=sumB[i-1];
            sumC[i]=sumC[i-1];
            
            char c=T[i-1];
            
            if(c=='Q') sumA[i]++;
            if(c=='B') sumB[i]++;
            if(c=='W') sumC[i]++;
        }
        
        int left=N-1,right=N+M+1;
        while(right-left>1){
            int mid=(left+right)/2;
            for(int i=0;i<=M;i++){
                for(int j=0;j<=sumA[i];j++){
                    mada[i][j]=false;
                    dp[i][j]=INF;
                }
            }
            if(mid==N){
                dp[0][sumA[0]]=sumC[0];
            }else{
                mada[0][0]=true;
            }
            
            for(int i=0;i<M;i++){
                for(int a=0;a<=min(i,sumA[i]);a++){
                    if(mada[i][a]){
                        int b=(i-a)/2;
                        int A=sumA[i]-a,B=sumB[i]-b,C=sumC[i];
                        if(A){
                            mada[i+1][a+1]=true;
                        }
                        if(B){
                            if(1+A+B+C+1==mid){
                                chmin(dp[min(i+2,M)][A+(T[i]=='Q')+(T[i+1]=='Q')],C+(T[i]=='W')+(T[i+1]=='W'));
                            }else{
                                mada[min(i+2,M)][a]=true;
                            }
                        }
                    }
                }
                
                for(int a=0;a<=min(mid,sumA[i]);a++){
                    if(dp[i][a]!=INF){
                        int c=dp[i][a],b=mid-1-a-c;
                        if(a){
                            chmin(dp[i+1][a-1+(T[i]=='Q')],c+(T[i]=='W'));
                        }
                        if(b){
                            chmin(dp[min(i+2,M)][a+(T[i]=='Q')],c+(T[i]=='W'));
                        }
                    }
                }
            }
            
            bool ok=false;
            
            for(int a=0;a<=sumA[M];a++){
                if(mada[M][a]) ok=true;
                if(dp[M][a]!=INF) ok=true;
            }
            
            if(ok) right=mid;
            else left=mid;
        }
        
        if(right<=N+M) cout<<right<<"\n";
        else cout<<"IMPOSSIBLE"<<"\n";
    }
}