20t-5t2=18,75

Solution for 20t-5t2=18,75 equation:

20t-5t^2=18.75

We move all terms to the left:

20t-5t^2-(18.75)=0

We add all the numbers together, and all the variables

-5t^2+20t-18.75=0

a = -5; b = 20; c = -18.75;
Δ = b2-4ac
Δ = 202-4·(-5)·(-18.75)
Δ = 25
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{25}=5$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(20)-5}{2*-5}=\frac{-25}{-10}
=2+1/2
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(20)+5}{2*-5}=\frac{-15}{-10}
=1+1/2
$