11th grade math factoring help please

Factor: 4a^2 + 11a - 20

Thanks! xoxo

It is

(4a - 5)(a + 4)

Start by setting up the possible ways you could get 4a^2

(2a.....)(2a.....) & (4a.....)(a.....)

Then find the different factors that would give 20

1 x 20, 2 x 10, 4 x 5

since the last number is negative, one of the second terms needs a negative sign, since the middle term is positive and an odd # it considerably reduces the number of possibilities.