0=20t-15t^2

Solution for 0=20t-15t^2 equation:

0=20t-15t^2

We move all terms to the left:

0-(20t-15t^2)=0

We add all the numbers together, and all the variables

-(20t-15t^2)=0

We get rid of parentheses

15t^2-20t=0

a = 15; b = -20; c = 0;
Δ = b2-4ac
Δ = -202-4·15·0
Δ = 400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{400}=20$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-20}{2*15}=\frac{0}{30}
=0
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+20}{2*15}=\frac{40}{30}
=1+1/3
$