Умножаем все на (x+6)(x-3)(x-6)
(x-3)(x-6) + 7(x+6)(x-6) = 5(x+6)(x-3)
x^2-9x+18 + 7(x^2-36) = 5(x^2+3x-18)
x^2 - 9x - 18 + 7x^2 - 252 = 5x^2 + 15x - 90
3x^2 -24x - 180 = 0
x^2 - 8x - 60 = 0
D/4 = 4^2 - (-60) = 16 + 60 = 76 = (2√19)^2
x1 = 4 - 2√19
x2 = 4 + 2√19