#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define endl '\n'
void GordenGhost();
int main(){
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int t=1;
    cin>>t;
    while(t--){
        GordenGhost();
    }
    return 0;
}

void GordenGhost(){
    int n,k,sum=0,ans=0,ww=0;
    vector<int>one,two;
    cin>>n>>k;
    for (int i = 0; i < n; ++i) {
        int a;
        cin>>a;
        one.push_back(a);
    }
    for (int i = 0; i < n; ++i) {
        int a;
        cin>>a;
        two.push_back(a);
    }
    for (int i = 0; i < min(k,n); ++i) {
        sum+=one[i];
        ww= max(ww,two[i]);
        ans= max(ans,sum+ww*(k-1-i));
    }
    cout<<ans<<endl;
}