// This Code was made by Chinese_zjc_.
#include <bits/stdc++.h>
// #define debug
int T, n, m, p[5005][5005], dp[5005][5005], c1[5005], c2[5005];
std::string s, t;
bool check(int size)
{
    for (int i = 0; i <= c1[n]; ++i)
    {
        int pos = p[i][size - m];
        if (pos && dp[pos][c1[pos] - i] <= c2[pos] - (size - m))
            return true;
    }
    return false;
}
signed main()
{
    std::ios::sync_with_stdio(false);
    std::cin >> T;
    while (T--)
    {
        std::cin >> m >> n >> t >> s;
        s = t + s;
        n = n + m;
        for (int i = 0; i != n; ++i)
        {
            c1[i + 1] = c1[i] + (s[i] == 'Q');
            c2[i + 1] = c2[i] + (s[i] == 'B');
        }
        for (int i = 0; i <= n; ++i)
            for (int j = 0; j <= n; ++j)
                p[i][j] = 0;
        p[0][0] = m;
        for (int i = 0; i <= c1[n]; ++i)
            for (int j = 0; j <= c2[n]; ++j)
            {
                if (i < c1[p[i][j]])
                    p[i + 1][j] = std::min(n, p[i][j] + 1);
                if (j < c2[p[i][j]])
                    p[i][j + 1] = std::min(n, p[i][j] + 2);
            }
        for (int i = 0; i <= n; ++i)
            dp[n][i] = 0;
        for (int i = n; i--;)
            for (int j = 0; j <= n; ++j)
            {
                dp[i][j] = INT_MAX / 2;
                if (j)
                    dp[i][j] = std::min(dp[i][j], dp[i + 1][j - 1 + (s[i] == 'Q')] - (s[i] == 'B'));
                dp[i][j] =
                    std::min(dp[i][j],
                             std::max(1,
                                      dp[std::min(n, i + 2)][j + (s[i] == 'Q')] - (s[i] == 'B') + 1));
            }
        // for (int i = 0; i <= c1[n]; ++i)
        //     for (int j = 0; j <= c2[n]; ++j)
        //         std::cout << p[i][j] << " \n"[j == c2[n]];
        // std::cout << c1[n] << ' ' << c2[n] << std::endl;
        if (p[c1[n]][c2[n]] == 0)
        {
            std::cout << "IMPOSSIBLE" << std::endl;
            continue;
        }
        // std::cout << check(3) << std::endl;
        int l = m, r = n;
        while (l < r)
        {
            int mid = (l + r) >> 1;
            if (check(mid))
                r = mid;
            else
                l = mid + 1;
        }
        std::cout << l << std::endl;
    }
    return 0;
}