-3x^2-3x=-90

Solution for -3x^2-3x=-90 equation:

-3x^2-3x=-90

We move all terms to the left:

-3x^2-3x-(-90)=0

We add all the numbers together, and all the variables

-3x^2-3x+90=0

a = -3; b = -3; c = +90;
Δ = b2-4ac
Δ = -32-4·(-3)·90
Δ = 1089
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1089}=33$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-3)-33}{2*-3}=\frac{-30}{-6}
=+5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-3)+33}{2*-3}=\frac{36}{-6}
=-6
$