#include <bits/stdc++.h>

inline int change(char a) {
  if (a == 'Q') return 1;
  if (a == 'B') return 2;
  return 0;
}

inline void update(int& a, int b) {
  a = std::min(a, std::max(0, b));
}

int main() {
  std::ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  std::cout.tie(nullptr);

  int testCase = 1;
  std::cin >> testCase;
  while (testCase--) {
    int N, M;
    std::cin >> N >> M;
    std::string S, T;
    std::cin >> S >> T;
    S = " " + S;
    T = " " + T;

    std::vector <int> A(M + 10, 0), prefOne(M + 10, 0), prefTwo(M + 10, 0), prefO(M + 10, 0);
    for (int i = 1; i <= M; ++i) {
      A[i] = change(T[i]);
      prefOne[i] = prefOne[i - 1] + (A[i] == 1);
      prefTwo[i] = prefTwo[i - 1] + (A[i] == 2);
      prefO[i] = prefO[i - 1] + (A[i] == 0);
    }

    for (int i = M + 1; i <= M + 2; ++i) {
      prefO[i] = prefO[i - 1];
      prefOne[i] = prefOne[i - 1];
      prefTwo[i] = prefTwo[i - 1];
    }

    std::array <int, 3> initial = {0, 0, 0};
    for (int i = 1; i <= N; ++i) {
      ++initial[change(S[i])];
    }

    std::vector <std::vector <int>> dp(M + 10, std::vector <int> (N + M + 50, 1e9)); //dp(i) : i~M, i has not been choosen
    for (int i = 0; i <= N + M + 5; ++i) {
      dp[M + 1][i] = dp[M + 2][i] = 0;
    }

    for (int i = M; i; --i) {
      for (int j = 0; j <= N + i; ++j) {
        if (A[i] == 0) {
          update(dp[i][j], dp[i + 1][j] + 1);
          if (j) {
            update(dp[i][j], dp[i + 2][j - 1]);
          }
        }

        if (A[i] == 1) {
          update(dp[i][j], dp[i + 1][j]);
          if (j) {
            update(dp[i][j], dp[i + 2][j - 1] - 1);
          }
        }

        if (A[i] == 2) {
          update(dp[i][j], dp[i + 1][j + 1] + 1);
          if (j) {
            update(dp[i][j], dp[i + 2][j]);
          }
        }
      }
    }

    auto calc =[&](int border, int cnts2) {
      return border - 2 * (initial[2] + prefTwo[border] - cnts2);
    };

    auto getOne =[&](int border, int cnts2) {
      return initial[1] + prefOne[border] - calc(border, cnts2);
    };

    std::vector <std::vector <int>> g(M + 10, std::vector <int> (M + N + 10, 0));// g : 1~i
    g[0][initial[2]] = 1;

    for (int i = 0; i <= M; ++i) {
      for (int j = 0; j <= N + i; ++j) {
        if (!g[i][j]) continue;
        int one = getOne(i, j);
        assert(one >= 0);
        if (one > 0) {
          if (A[i + 1] != 2) {
            g[i + 1][j] = 1;
          } else {
            g[i + 1][j + 1] = 1;
          }
        }

        if (j > 0) {
          if (prefTwo[i + 2] - prefTwo[i] == 0) {
            g[i + 2][j - 1] = 1;
          } else {
            g[i + 2][j - 1 + prefTwo[i + 2] - prefTwo[i]] = 1;
          }
        }
      }
    }

    int best = 1e9;
    for (int i = 0; i <= M; ++i) {
      for (int j = 0; j <= N + i; ++j) {
        if (!g[i][j]) continue;
        int one = getOne(i, j);
        if (one >= dp[i + 1][j]) {
          best = std::min(best, j + one + prefO[i] + initial[0]);
        }
      }
    }
    
    if (best != 1e9)
      std::cout << best << '\n';
    else 
      std::cout << "IMPOSSIBLE\n";
  }

  return 0;
}