All you have to do is find the multiples of 3 and 4.
3: 3, 6, 9, 12
4: 4, 8, 12
You will notice that both have twelve in there multiples so you can only count 1, and you are left with 6 numbers, therfore you are left with 6 out of 13 of the tiles are a multiples of 3 and 4.
The answer is 6(N+12) This is because it is telling you that the equation is six times a SUM of a number and twelve. So the number and 12 added together are multiplied by 6.
