from heapq import*
Q = []
for _ in range(int(input())):
  n,k = map(int,input().split())
  A = list(map(int,input().split()))
  s = sum(a%k for a in A)
  m = max(a%k for a in A)
  if s%k:
    print(-1)
    continue
  s //= k
  for a in A:
    heappush(Q,a)
  for _ in range(max(m-s,0)):
    a = heappop(Q)
    heappush(Q,a-k)
  if Q[0]<0:
    print(-1)
  else:
    print(max(m,s))