from collections import deque def solve(): n, K = map(int, input().split()) A = list(map(int, input().split())) A.sort() C = [a % K for a in A] if sum(C) % K != 0: print(-1) return queue = deque() pos = [[] for _ in range(K)] for i, c in enumerate(C): pos[c].append(i) for row in pos: queue.extend(row) tot = sum(C) // K ma = max(C) cnt = K * K + 10 while ma > tot and cnt > 0 and queue: i = queue.popleft() if A[i] == C[i]: continue cnt -= 1 C[i] += K tot += 1 ma = C[i] queue.append(i) if ma <= tot: print(tot) else: print(-1) for _ in range(int(input())): solve()