We need to solve the following equation for x, and choose the positive solution
[tex]4x^2+12x=135[/tex]we substract 135 from both sides of the equation obtaining the canonical form of a quadratic equation, the we apply the quadratic formula with a=4, b=12 and c=-135 then x will be equal to:
[tex]x=\frac{-12+\sqrt[]{144-4(4)(-135)}}{8}=\frac{48-12}{8}=\frac{9}{2}=4.5[/tex]