import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
#######################################################################

for _ in range(ni()):
    n, k = na()
    a = sorted(na())

    if sum(a) % k:
        print(-1)
        continue
    
    def check(r):
        z = 0
        y = 0
        for i in range(n):
            if a[i] % k > r:
                return False
            z += a[i] % k
            z += (min(a[i], r) - a[i] % k) // k * k
        return z >= r * k
    
    for i in range(10 ** 9):
        if check(i):
            print(i)
            break