-99=63u-36u^2

Solution for -99=63u-36u^2 equation:

-99=63u-36u^2

We move all terms to the left:

-99-(63u-36u^2)=0

We get rid of parentheses

36u^2-63u-99=0

a = 36; b = -63; c = -99;
Δ = b2-4ac
Δ = -632-4·36·(-99)
Δ = 18225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{18225}=135$
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-63)-135}{2*36}=\frac{-72}{72}
=-1
$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-63)+135}{2*36}=\frac{198}{72}
=2+3/4
$