resolver: (3-X) (X+4)+16=12X-(X+3)2
(3-X) (X+4)+16=12X-(X+3)^2
3x+12-x^2-4x=12x-x^2+6x-9
-x^2-x+12=-x^2+18x-9
-x^2-x+x^2-18x=-12+9
19x=-3
x=-3/19
Espero te sirva :D
