4x(3x+15)=90

Solution for 4x(3x+15)=90 equation:

4x(3x+15)=90

We move all terms to the left:

4x(3x+15)-(90)=0

We multiply parentheses

12x^2+60x-90=0

a = 12; b = 60; c = -90;
Δ = b2-4ac
Δ = 602-4·12·(-90)
Δ = 7920
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:

$\sqrt{\Delta}=\sqrt{7920}=\sqrt{144*55}=\sqrt{144}*\sqrt{55}=12\sqrt{55}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(60)-12\sqrt{55}}{2*12}=\frac{-60-12\sqrt{55}}{24}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(60)+12\sqrt{55}}{2*12}=\frac{-60+12\sqrt{55}}{24}
$