T=int(input())
for _ in range(T):
  X,M=map(int,input().split())
  lx=len(str(X))
  q=[-1]*10**lx
  for i in range(1000):
    j=(M*i)%(10**lx)
    if q[j]==-1:
      q[j]=M*i
  ans=-1
  Y=X*(10**15)
  Y+=(-Y)%M
  Y+=q[(X-Y)%(10**lx)]
  ly=len(str(Y))
  if Y%M==0 and lx<=ly<=18 and str(Y)[:lx]==str(Y)[-lx:]==str(X):
    ans=Y
  print(ans)