#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 = 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;
};
auto get = [&] (string s, int mid) -> ll {
int ka = mid, kb = k - mid;
for(int i = 0; i < n && ka > 0; i++) {
if(s[i] == '?') {
s[i] = 'A';
--ka;
}
}
for(int i = n - 1; i >= 0 && kb > 0; i--) {
if(s[i] == '?') {
s[i] = 'B';
--kb;
}
}
return calAns(s);
};
ans = get(s1, 0); // Initial ans
int lo = 0, hi = k, mid;
while(lo <= hi) {
mid = lo + hi >> 1;
ll cur = get(s1, mid);
if(ans <= cur) {
ans = cur;
lo = mid + 1;
}
else hi = mid - 1;
}
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;
}