Tìm x: x - (x - 3) - 12 + 4x = 0

Tìm x: 

a) x - (x-3) - 12 + 4x = 0

b) (x-4)(x^2 + 4x + 16) - x (x^2 - 6) = -4 

c) x^2 - 10x = 11