#include<bits/stdc++.h>
#define endl        '\n'
#define F           first
#define S           second
#define pb          push_back
#define yes         cout<<"YES\n"
#define no          cout<<"NO\n"
#define all(x)      x.begin(),x.end()
#define allr(x)     x.rbegin(),x.rend()
#define error1(x)   cerr<<#x<<" = "<<(x)<<endl
#define error2(a,b) cerr<<"("<<#a<<", "<<#b<<") = ("<<(a)<<", "<<(b)<<")\n";
#define coutall(v)  for(auto &it: v) cout << it << " "; cout << endl;
using namespace std;
using ll = long long;
using ld = long double;

void solve() {
    ll n, k, ans = 0;
    string s1;
    cin >> n >> k >> s1;
    k = min(k, (ll)count(all(s1), '?'));

    auto calAns = [&](string &s) -> ll {
        ll cntB = (ll)count(all(s), 'B'), tot = 0;
        for(int i = 0; i < n; i++) {
            if(s[i] == 'A') tot += cntB;
            else if(s[i] == 'B') --cntB;
        }
        return tot;
    };

    if(k == 1) {
        for(int i = 0; i < n; i++) { // first ? -> A
            if(s1[i] == '?') {
                s1[i] = 'A';
                ans = max(ans, calAns(s1));
                s1[i] = '?';
                break;
            }
        }
        for(int i = n - 1; i >= 0; i--) { // last ? -> B
            if(s1[i] == '?') {
                s1[i] = 'B';
                ans = max(ans, calAns(s1));
                s1[i] = '?';
                break;
            }
        }
    }
    else if(k > 1) {
        string tmp = s1;

        int a = (k + 1) >> 1, b = k >> 1;
        for(int i = 0; i < n && a > 0; i++) {
            if(s1[i] == '?') {
                s1[i] = 'A';
                --a;
            }
        }
        for(int i = n - 1; i >= 0 && b > 0; i--) {
            if(s1[i] == '?') {
                s1[i] = 'B';
                --b;
            }
        }
        ans = max(ans, calAns(s1));

        int cntA = 0, cntB = count(all(tmp), 'B');
        for(int i = 0; i < n && k > 0; i++) {
            if(tmp[i] == '?') {
                --k;
                if(cntA <= cntB) tmp[i] = 'A', ++cntA;
                else tmp[i] = 'B';
            }
            else if(tmp[i] == 'A') ++cntA;
            else if(tmp[i] == 'B') --cntB;
        }
        ans = max(ans, calAns(tmp));
    }
    else ans = max(ans, calAns(s1));

    cout << ans << endl;
    return;
}

signed main() {
    ios::sync_with_stdio(false); cin.tie(0);
    int tc = 1;
    cin >> tc;
    for (int t = 1; t <= tc; t++) {
        // cout << "Case " << t << ": ";
        solve();
    }
    return 0;
}