iiitv/ChefLib

// Code written by Monal
#include "bits/stdc++.h"

using namespace std;

int main() {
    ios::sync_with_stdio(false);
    int tc;
    cin>>tc;
    while (tc--) {
        long long int n,k;
        cin>>n>>k;
        string s;
        cin>>s;
        long long int aarr[n];
        long long int barr[n];
        memset(aarr,0,n);
        memset(barr,0,n);
        long long int answer = 0;
        long long int count=0;
        for (long long int i=0;i<n;++i) {
            if (s[i]=='b')
                count++;
            else if (s[i]=='a')
                barr[i]=count;
        }
        count=0;
        for (long long int i=n-1;i>=0;--i) {
            if (s[i]=='b')
                count++;
            else if (s[i]=='a')
                aarr[i]=count;
        }
        for (long int i=0;i<n;++i) {
            if (s[i]=='a') {
                //cout<<"i:"<<i<<endl;
                answer += ((aarr[i]*k*(k+1))/2);
                //cout<<"after b:"<<((aarr[i]*k*(k+1))/2)<<endl;
                answer += ((barr[i]*k*(k-1))/2);
                //cout<<"before b:"<<((barr[i]*k*(k-1))/2)<<endl;
            }
        }
        cout<<answer<<"\n";
    }
    return 0;
}