#include <bits/stdc++.h>
using namespace std;

#define FAST ios_base::sync_with_stdio(false);cin.tie(NULL);
using ll = long long;

int main() {
  FAST;
  
  int tc = 1, ti;
  cin >> tc;

  for (ti = 1; ti <= tc; ++ti) {
    ll n, k, i, l, r, ans;
    string s;
    cin >> n >> k;
    cin >> s;
    s = " " + s;

    vector<ll> pa(n+1, 0), pb(n+1, 0), pq(n+1, 0);
    for (i = 1; i <= n; ++i) {
      pa[i] = pa[i-1];
      pb[i] = pb[i-1];
      pq[i] = pq[i-1];
      if (s[i] == 'A') pa[i] += 1;
        else if (s[i] == 'B') pb[i] += 1;
        else if (s[i] == '?') pq[i] += 1;
    }
    k = min(k, pq[n]);

    auto get_ans = [&](ll i, ll qa, ll qb) -> ll {
      // all '?' in s[1...i] = 'a'
      // all '?' in s[i+1...n] = 'b'

      ll curr = 0;

      // a -> b
      l = pa[i];
      r = pb[n] - pb[i];
      curr += l*r;

      // a -> ?
      l = pa[i];
      r = min(qb, pq[n] - pq[i]);
      curr += l*r;

      // ? -> b
      l = min(qa, pq[i]);
      r = pb[n] - pb[i];
      curr += l*r;

      // ? -> ?
      l = min(qa, pq[i]);
      r = min(qb, pq[n] - pq[i]);
      curr += l*r;

      return curr;
    };

    ans = 0;
    for (i = 1; i <= n; ++i) {
      ans = max(ans, get_ans(i, k/2, k-k/2));
      ans = max(ans, get_ans(i, (k+1)/2, k-(k+1)/2));
    }

    cout << ans << "\n";
  }

  return 0;
}