package com.company;
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
// write your code here
int t;
Scanner s=new Scanner(System.in);
t=s.nextInt();
int o[]=new int[t];
for(int i=0;i<t;i++) {
int n, k;
int v, av, av1;
n = s.nextInt();
k = s.nextInt();
v = s.nextInt();
int a[] = new int[n];
for (int j = 0; j < n; j++) {
a[j] = s.nextInt();
}
int sum = 0;
for (int j = 0; j < n; j++) {
sum = sum + a[j];
}
o[i] = (v * (n + k) - sum) / k;
boolean dec = (v * (n + k) - sum) % k == 0;
if (o[i] < 1 || !dec) {
o[i]=-1;
}
}
for(int i =0;i<t;i++)
System.out.println(o[i]);
}
}