Question 40838
The watchwords here are to factor and cancel, factor and cancel, factor and cancel...so from
(4r^2 - 25s^2) / (2r^2 + 3rs - 20s^2) =
(2r + 5s)(2r - 5s) / (2r - 5s)(r + 4s) = 
(2r + 5s) / (r + 4s)