To factor the trinomial, you can use the ac method where you multiply the first and last terms together (6 and 9) and add up to 15. In this case ac= 54 2 numbers that multiply to 54 and add up to 15 would be 6 and 9 so place these numbers where the 15 would be:
Then group terms to simplify:
Simplify any like terms:
And group together again:
You can simplify a 3 out of the first expression one more time to get:
Which would be the factored form. I hope this helps :)