60=5t^2+20t

Solution for 60=5t^2+20t equation:

60=5t^2+20t

We move all terms to the left:

60-(5t^2+20t)=0

We get rid of parentheses

-5t^2-20t+60=0

a = -5; b = -20; c = +60;
Δ = b2-4ac
Δ = -202-4·(-5)·60
Δ = 1600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1600}=40$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-40}{2*-5}=\frac{-20}{-10}
=+2
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+40}{2*-5}=\frac{60}{-10}
=-6
$