(3x + 12)(x + 4) = (4x^2 + 8x + 18x^2)/(2x) { assuming that x is not 0 }
3x^2 + 12x + 12x + 48 = (2x) (2x + 4 + 9x) / (2x)
3x^2 + 24x + 48 = 11x + 4
3x^2 + 13x + 44 = 0
Using the Q formula
-13 ±√ [ 13^2 - 4 * 3 * 44 ] 13±√ -359 13 ± i√ 359
x = ______________________ = _________ = __________
2 * 3 6 6