Answer: 27a + 25
I think I did it right, I'm not too sure though. Sorry! :(

Annissa

You'd distribute first to get:
= (15a + 15) + (12a + 10)
Then you don't need parenthesis anymore so you can remove those:
= 15a + 15 + 12a+ 10
Then just add up the liked terms:
= 27a + 25