#include<bits/stdc++.h>
using namespace std;
const int N = 5e3 + 5;

char str1[N],str2[N];
void cg(int &idx, int &nowb, int &nowq)
{
    if(str2[idx] == 'B') nowb ++;
    if(str2[idx] == 'Q') nowq ++;
    idx ++;
}

void solve()
{
    int n,m,i,bnum=0,qnum=0,now,nowb,nowq,nown;
    scanf("%d%d",&n,&m);
    scanf("%s%s",str1+1,str2+1);
    for(i=1;i<=n;i++)
    {
        if(str1[i] == 'B') bnum ++;
        if(str1[i] == 'Q') qnum ++;
    }
    for(i=n;i<=n+m;i++)
    {
        nowb = bnum; nowq = qnum; now = 1; nown = n;
        while(now <= m && nown < i)
        {
            if(nowb)
            {
                nown ++; nowb --;
                cg(now,nowb,nowq);
                cg(now,nowb,nowq);
            }
            else if(nowq)
            {
                nowq --;
                cg(now,nowb,nowq);
            }
            else break;
        }
        if(nown < i && now <= m) break;
        while(now <= m)
        {
            if(!nowq && !nowb) break;
            if(now+1 > m)
            {
                now ++; break;
            }
            if(!nowq || (str2[now+1] == 'W' && nowb))
            {
                nowb --;
                cg(now,nowb,nowq);
                now ++;
            }
            else
            {
                nowq --;
                cg(now,nowb,nowq);
            }
        }
        if(now > m)
        {
            printf("%d\n",i); return;
        }
    }
    printf("IMPOSSIBLE\n");
}

int main()
{
    int T=1;
    scanf("%d",&T);
    while(T--) solve();
    return 0;
}