-3(5a+3)+6a-4

I'm assuming you want to simplify the expression. Use the distributive property to distribute the -3 to the two terms inside the parenthesis. In other words, you will need to multiply -3 by 5a and then -3 by 3.

You should end up with: -15a - 9 + 6a - 4

Now simply add the like terms together for the final answer.