#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define Mp make_pair
#define pb push_back
#define SZ(a) (int(a.size()))

typedef long long ll;
typedef double db;
typedef std::pair<int, int> pii;
typedef std::vector<int> vi;
std::mt19937_64 gen(std::chrono::system_clock::now().time_since_epoch().count());
ll get(ll l, ll r) { std::uniform_int_distribution<ll> dist(l, r); return dist(gen); }

void solve() {
    int n, m;
    cin >> n >> m;
    string hand, s;
    cin >> hand >> s;
    hand = ' ' + hand;
    s = ' ' + s;

    vi hcnt(3);
    for(auto ch : hand) {
        if(ch == 'Q') hcnt[1]++;
        else if(ch == 'B') hcnt[2]++;
        else if(ch == 'W') hcnt[0]++;
    }
    n--;
    vi disk(m + 1);
    vector sum(m + 1, vi(3));
    for(int i = 1; i <= m; i++) {
        if(s[i] == 'Q') disk[i] = 1;
        else if(s[i] == 'B') disk[i] = 2;
        else if(s[i] == 'W') disk[i] = 0;
        sum[i] = sum[i - 1];
        sum[i][disk[i]]++;
    }

    const int inf = 1e9;
    vector f(m + 10, vi(n + m + 10, inf)), g(m + 10, vi(n + m + 10));
    g[0][hcnt[2]] = 1;
    for(int i = 0; i < m; i++) {
        for(int j = 0; j <= n + m; j++) {
            if(g[i][j] == 0) continue;
            int c2all = hcnt[2] + sum[i][2] - j;
            int c1use = i - c2all * 2;
            int c1 = hcnt[1] + sum[i][1] - c1use;
            if(c1) {
                g[i + 1][j + (disk[i + 1] == 2)] = 1;
            }
            if(j && i + 2 < m) {
                g[i + 2][j - 1 + (disk[i + 1] == 2) + (disk[i + 2] == 2)] = 1;
            }
        }
    }
    // for(int i = 0; i <= m; i++)
    //     for(int j = 0; j <= n + m; j++) {
    //         if(g[i][j]) {
    //             cout << i << ' ' << j << '\n';
    //         }
    //     }
    // cout << '\n';
    for(int j = 0; j <= n + m; j++) {
        f[m][j] = f[m + 1][j] = 0;
    }
    for(int i = m - 1; i >= 0; i--) {
        for(int j = 0; j <= n + m; j++) {
            if(disk[i + 1] == 2) {
                f[i][j] = min(f[i][j], f[i + 1][j + 1] + 1);
                if(j) f[i][j] = min(f[i][j], f[i + 2][j]);
            } else if(disk[i + 1] == 1) {
                f[i][j] = min(f[i][j], max(f[i + 1][j], 1));
                if(j) f[i][j] = min(f[i][j], max(f[i + 2][j - 1] - 1, 0));
            } else {
                f[i][j] = min(f[i][j], f[i + 1][j] + 1);
                if(j) f[i][j] = min(f[i][j], f[i + 2][j] + 1);
            }
            // f[i][j] = min(
            //     max(f[i + 1][j] + 1 - (disk[i + 1] == 1), 1), // use [1]
            //     j ? f[i + 2][j - 1] - (disk[i + 1] == 1) : inf // use [2]
            // );
            // cout << i << ' ' << j << ' ' << f[i][j] << '\n';
        }
    }
    
    for(int k = n; k <= n + m; k++) {
        int fl = 0;
        for(int t = 0; t < m; t++) {
            int tot = n + t;
            int c0 = hcnt[0] + sum[t][0];
            int c2 = hcnt[2] + sum[t][2] - (k - n);
            int c1 = hcnt[1] + sum[t][1] - t + 2 * (k - n);
            if(c1 >= 0 && c2 >= 0 && g[t][c2] && f[t][c2] <= c1) {
                cout << k << ' ' << t << ' ' << c0 << ' ' 
                    << c1 << ' ' << c2 << ' ' << f[t][c2] << '\n';
                fl = 1;
                break;
            }
        }
        if(fl) {
            cout << k << '\n';
            return;
        }
    }
    cout << "IMPOSSIBLE\n";
}
signed main() {
    atexit([](){cerr << "time: " << (db)clock()/CLOCKS_PER_SEC << "s\n";});
    ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
    int t = 1;
    cin >> t;
    while(t--) solve();
    return 0;
}