(10x+15)(5x)=90

Solution for (10x+15)(5x)=90 equation:

(10x+15)(5x)=90

We move all terms to the left:

(10x+15)(5x)-(90)=0

We multiply parentheses

50x^2+75x-90=0

a = 50; b = 75; c = -90;
Δ = b2-4ac
Δ = 752-4·50·(-90)
Δ = 23625
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:

$\sqrt{\Delta}=\sqrt{23625}=\sqrt{225*105}=\sqrt{225}*\sqrt{105}=15\sqrt{105}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(75)-15\sqrt{105}}{2*50}=\frac{-75-15\sqrt{105}}{100}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(75)+15\sqrt{105}}{2*50}=\frac{-75+15\sqrt{105}}{100}
$