3(x^2+5x-20)=0

Solution for 3(x^2+5x-20)=0 equation:

3(x^2+5x-20)=0

We multiply parentheses

3x^2+15x-60=0

a = 3; b = 15; c = -60;
Δ = b2-4ac
Δ = 152-4·3·(-60)
Δ = 945
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:

$\sqrt{\Delta}=\sqrt{945}=\sqrt{9*105}=\sqrt{9}*\sqrt{105}=3\sqrt{105}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(15)-3\sqrt{105}}{2*3}=\frac{-15-3\sqrt{105}}{6}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(15)+3\sqrt{105}}{2*3}=\frac{-15+3\sqrt{105}}{6}
$