q=[[[-1]*10**l for i in range(1000)] for l in range(4)]
for l in range(1,4):
  for m in range(1000):
    for i in range(1000):
      j=(m*i)%(10**l)
      if q[l][m][j]==-1:
        q[l][m][j]=i
T=int(input())
for _ in range(T):
  X,M=map(int,input().split())
  lx=len(str(X))
  ans=-1
  Y=X*(10**15)
  Y+=(-Y)%M
  Y+=M*q[lx][M%1000][(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)