T=int(input())
ans=[]
for _ in range(T):
    N,K=map(int,input().split())
    A=list(map(int,input().split()))
    cand=10**30
    cur=1
    for i in range(N):
        for j in range(N):
            if i==j:
                cur*=A[j]-K
            else:
                cur*=A[j]
        cand=min(cand,cur)
    ans.append(cand)
import sys
sys.stdout.write('\n'.join(map(str,ans)))