(2n + 5k)^2 = (2n + 5k)(2n + 5k)
Here we need to use FOIL
First - 2n * 2n = 4n^2
Outside - 2n * 5k = 10nk
Inside - 5k * 2n = 10nk
Last - 5k * 5k = 25k^2
That gives us 4n^2 + 10nk + 10nk + 25k^2, we can combine 10nk + 10nk to give 20nk, and a final equaion of 4n^2 + 20nk + 25k^2
