Show all work and factor completely.

6a^2+5a-4
(6a^2+8a)-(3a-4)
2a(3a+4)-1(3a+4)
(3a+4)(2a+1)
Is this correct?

close to the very end

is (2a+1) a typo

from your second last line you should have seen that it had to be
(3a+4)(2a-1)

btw, you can always check your answers to this type of question by expanding your answer.