Answer:
18 goals this season.
Explanation:
First, we must identify what the question is asking.
13 goals last season, 5 more this season.
How many this season?
Well, if he scored more this season, we know this is going to be an addition problem.
Since he scored 13 last season a 5 more this season, we must add 13 and 5.
13 + 5 = 18 :D