import java.util.*;
import java.io.*;
public class Main {

    static StreamTokenizer st = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
    static PrintWriter pw = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
    public static void main(String[] args)throws Exception {
        int q = Int();
        while (q-- > 0) {
            int n = Int();
            int k = Int();
            int[] a = new int[n];
            int[] b = new int[n];
            a[0]=Int();
            for (int i = 1; i < n; i++) a[i] =a[i-1]+ Int();
            b[0]=Int();
            int max2=b[0];
            for (int i = 1; i < n; i++) max2=b[i] = Math.max(Int(),max2);
            int j=Math.min(k,a.length);
            int max=0;
            for(int i=j-1;i>=0;i--){
                int sum=0;
                int m=k-i-1;
                sum+=a[i];
                if(m==0)max= Math.max(sum,max);
                else {
                    sum += b[i] * m;
                    max = Math.max(sum, max);
                }
            }
            pw.println(max);
        }
        pw.flush();
    }
    private static int Int() throws Exception{
        st.nextToken();
        return (int)st.nval;
    }
}