a, 3^3 . x^2 - 2^4 . x^2 = 8^2 . 5 - 4^2 . 3^2
27 . x^2 - 16 . x^2 = 64 . 5 - 16 . 9
(27 - 16) . x^2 = 320 - 144
11 . x^2 = 176
x^2 = 176 ÷ 11 = 16
x = $\sqrt[]{16}$ = 4
b, 3^2 . x^2 - 2^2 . x^2 = 3^3 . 5 - (255 : 51) .11
9 . x^2 - 4 . x^2 = 27 . 5 - 5 . 11
(9 - 4) . x^2 = (27 - 11) . 5
5 . x^2 = 16 . 5
=> x^2 = 16
x = $\sqrt[]{16}$ = 4