You have to extract common factor 3a^2
=> 3a^2 (5 x^2 + 4x + 3)
If you need help to know where each term inside the parenthesis come from, this is hoy you do it:
15a^2x^2
------------- = 5x^2
3a^2
12a^2x
----------- = 4x
3a^2
9a^2
-------- = 3
3a^2
Answer: 3a^2 (5x^2 + 4x + 3)
