` a) ` ` (x + 4)(x^2 - 4x + 16) - x(x - 5)(x + 5) = 264 `
` <=> x^3 - 4x^2 + 16x + 4x^2 - 16x + 64 - x(x^2 - 5^2) = 264 `
` <=> x^3 + 64 - x^3 + 25x = 264 `
` <=> 64 + 25x = 264 `
` <=> 25x = 200 `
` <=> x = 8 `
` b) ` ` (x - 2)^3 - (x - 2)(x^2 + 2x + 4) + 6(x - 2)(x + 2) = 60 `
` <=> x^3 - 3.x^{2}.2 + 3.x.2^2 - (x^3 + 2x^2 + 4x -2x^2 - 4x - 8) + 6(x^2 - 2^2) = 60 `
` <=> x^3 - 6x^2 + 12x - x^3 + 8 + 6x^2 - 24 = 60 `
` <=> 12x - 16 = 60 `
` <=> 12x = 72 `
` <=> x = 6 `
