Question 101334
3a+4b-(-6a-3b) = 3a+4b+6a+3b because the negative sign in front of the parentheses indicates that, when you remove the parentheses, you should multiply every term within the parentheses by -1 and so, -1(-6a) = +6a and -1(-3b) = +3b, so you get:
3a+4b+6a+3b = 9a+7b