Explanation:
Technically this expression is 15 as is.
You could add the parenthesis around the 3x4 or the 5-2.
So your answer is either:
(3x4) + 5 - 2
or 3x4 + (5-2)
OR (3x4) + (5-2)
But in my opinion, you do not want to have too many sets of parenthesis, it crowds your equation too much.