(x+6)(5x)=90

Solution for (x+6)(5x)=90 equation:

(x+6)(5x)=90

We move all terms to the left:

(x+6)(5x)-(90)=0

We multiply parentheses

5x^2+30x-90=0

a = 5; b = 30; c = -90;
Δ = b2-4ac
Δ = 302-4·5·(-90)
Δ = 2700
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{2700}=\sqrt{900*3}=\sqrt{900}*\sqrt{3}=30\sqrt{3}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(30)-30\sqrt{3}}{2*5}=\frac{-30-30\sqrt{3}}{10}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(30)+30\sqrt{3}}{2*5}=\frac{-30+30\sqrt{3}}{10}
$