T=int(input())
for _ in range(T):
  X,M=map(int,input().split())
  q=[-1]*1000
  for i in range(1000):
    j=(M*i)%1000
    if q[j]==-1:
      q[j]=M*i
  for i in range(20):
    Y=X*(10**i)
    Y+=(-Y)%M
    j=(X-Y)%1000
    if q[j]!=-1:
      Y+=q[j]
      if Y%M==0 and len(str(X))<=len(str(Y))<=18 and str(Y)[:len(str(X))]==str(Y)[-len(str(X)):]==str(X):
        print(Y)
        break
  else:
    print(-1)