#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
typedef long long int ll;


using namespace std;
using namespace __gnu_pbds;
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
#define mod 1000000007

ll lcm(ll a,ll b)
{
    return (a*b)/__gcd(a,b);
}


ll binExp(ll a,ll b)
{
    if(b==0)
        return 1;

    ll res=binExp(a,b/2);

    if(b&1)
    {
        return (a*res*res)%mod;

    }
    else
    {
        return (res*res)%mod;
    }
}


bool isPrime(long long  n)
{
    if (n <= 1)
        return false;
    if (n <= 3)
        return true;
    if (n % 2 == 0 || n % 3 == 0)
        return false;

    for (long long i = 5; i * i <= n; i += 6)
    {
        if (n % i == 0 || n % (i + 2) == 0)
            return false;
    }

    return true;
}

class DisjointSet
{

public:
    vector<ll> parent,rnk,sz;
    DisjointSet(ll n)
    {
        rnk.resize(n+1,0);
        parent.resize(n+1);
        sz.resize(n+1);

        for(ll i=0; i<=n; i++)
        {
            parent[i]=i;
            sz[i]=1;
        }
    }

    ll findUPar(ll node)
    {
        if(node==parent[node])
        {
            return node;
        }
        return parent[node]=findUPar(parent[node]);
    }

    bool unionByRank(ll u,ll v)
    {
        ll ulp_u=findUPar(u);
        ll ulp_v=findUPar(v);

        if(ulp_u==ulp_v)
        {
            return false;
        }
        if(rnk[ulp_u]==rnk[ulp_v])
        {
            parent[ulp_u]=ulp_v;
            rnk[ulp_v]++;
        }
        else if(rnk[ulp_u]<rnk[ulp_v])
        {
            parent[ulp_u]=ulp_v;
        }
        else if(rnk[ulp_v]<rnk[ulp_u])
        {
            parent[ulp_v]=ulp_u;
        }
        return true;
    }

    bool unionBYSize(ll u,ll v)
    {
        ll ulp_u=findUPar(u);
        ll ulp_v=findUPar(v);
        if(ulp_u==ulp_v)
            return false;

        if(sz[ulp_u]<sz[ulp_v])
        {
            parent[ulp_u]=ulp_v;
            sz[ulp_v]+=sz[ulp_u];
        }
        else
        {
            parent[ulp_v]=ulp_u;
            sz[ulp_v]+=sz[ulp_u];
        }
        return true;
    }




};





void solve()
{
    ll n,k;
    cin>>n>>k;


    string str;
    cin>>str;

    ll numA[n];
    ll numB[n];

    ll sumA=0;
    ll sumB=0;
    ll cnt=0;

    for(ll i=0; i<n; i++)
    {

        if(str[i]=='A')
        {
            sumA++;
        }
        else if(str[i]=='B')
        {
            sumB++;
        }
        else if(str[i]=='?')
        {
            cnt++;
        }
        numA[i]=sumA;
        numB[i]=sumB;
    }

    ll xx=min(cnt,k);
    ll i=0;
    while(i<n && xx>0)
    {
        if(str[i]=='?')
        {
            xx--;
            ll temp1=numB[n-1]-numB[i];

            ll temp2=0;
            if(i-1>=0)
               temp2=numA[i-1];
            if(temp1>temp2)
            {
                str[i]='A';
            }
            else if(temp2>=temp1)
            {
                str[i]='B';
            }

        }


        i++;
    }

    ll cntB[n];

    ll sum=0;

    for(ll i=n-1; i>=0; i--)
    {
        if(str[i]=='B')
        {
            sum++;
        }
        cntB[i]=sum;
    }

    ll ans=0;

    for(ll i=0; i<n; i++)
    {
        if(str[i]=='A')
        {
            ans+=(cntB[i]);
        }
    }
    cout<<ans<<endl;


}


























int main()
{


    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);





    ll t;

   cin>>t;
   //t=1;






    ll caseNo=1;



    while(t--)
    {
        //cout<<"Case "<<caseNo<<": ";
        // caseNo++;

        solve();


    }


    return 0;




}