-6n(-5-2n)=90

Solution for -6n(-5-2n)=90 equation:

-6n(-5-2n)=90

We move all terms to the left:

-6n(-5-2n)-(90)=0

We add all the numbers together, and all the variables

-6n(-2n-5)-90=0

We multiply parentheses

12n^2+30n-90=0

a = 12; b = 30; c = -90;
Δ = b2-4ac
Δ = 302-4·12·(-90)
Δ = 5220
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{5220}=\sqrt{36*145}=\sqrt{36}*\sqrt{145}=6\sqrt{145}$
$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(30)-6\sqrt{145}}{2*12}=\frac{-30-6\sqrt{145}}{24}
$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(30)+6\sqrt{145}}{2*12}=\frac{-30+6\sqrt{145}}{24}
$