(2x+6)(4x)=90

Solution for (2x+6)(4x)=90 equation:

(2x+6)(4x)=90

We move all terms to the left:

(2x+6)(4x)-(90)=0

We multiply parentheses

8x^2+24x-90=0

a = 8; b = 24; c = -90;
Δ = b2-4ac
Δ = 242-4·8·(-90)
Δ = 3456
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:

$\sqrt{\Delta}=\sqrt{3456}=\sqrt{576*6}=\sqrt{576}*\sqrt{6}=24\sqrt{6}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(24)-24\sqrt{6}}{2*8}=\frac{-24-24\sqrt{6}}{16}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(24)+24\sqrt{6}}{2*8}=\frac{-24+24\sqrt{6}}{16}
$