99=60x+4X^2

Solution for 99=60x+4X^2 equation:

99=60x+4x^2

We move all terms to the left:

99-(60x+4x^2)=0

We get rid of parentheses

-4x^2-60x+99=0

a = -4; b = -60; c = +99;
Δ = b2-4ac
Δ = -602-4·(-4)·99
Δ = 5184
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{5184}=72$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-60)-72}{2*-4}=\frac{-12}{-8}
=1+1/2
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-60)+72}{2*-4}=\frac{132}{-8}
=-16+1/2
$