First, you should probably solve the equation.
3 x 45 = 135
So n = 135.
For a division problem to work, the bigger number has to come first, so there are two possible answers.
135 / 45 = 3
135 / 3 = 45
Now all you need to do is put the n back in.
n / 45 = 3
n / 3 = 45