5/2 = 6/(x+4)² solve using square root principle

(Rationalize denominator in the answer)
Solve using the square root principle...
I cant get this one!
Thanks
The answer is
x=-20 +/- 2√15/5

5 / 2 = 6 / (x + 4)^2

cross multiply

5(x + 4)^2 = 12
(x + 4)^2 = 12/5
x + 4 = ± √(12/5)
x + 4 = ± √12 / √5
x + 4 = ± 2√3 / √5
x + 4 = ± 2√15 / 5
x = -4 ± (2√15 / 5)
x = (-20 ± 2√15) / 5