#include <iostream>
#include <cstdio>
using namespace std;

int main() {
	int t, n, x, b, s, min;
	scanf("%d", &t);
	while(t--) {
		scanf("%d %d", &n, &x);
		s=0; min=101;
		while(n--) { scanf("%d", &b); s=s+b; if(b<min) min=b; }
		if(min<=s%x) printf("-1\n");
		else printf("%d\n", s/x);
	}
	return 0;
}