20=5x^2-30x+45

Solution for 20=5x^2-30x+45 equation:

20=5x^2-30x+45

We move all terms to the left:

20-(5x^2-30x+45)=0

We get rid of parentheses

-5x^2+30x-45+20=0

We add all the numbers together, and all the variables

-5x^2+30x-25=0

a = -5; b = 30; c = -25;
Δ = b2-4ac
Δ = 302-4·(-5)·(-25)
Δ = 400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{400}=20$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(30)-20}{2*-5}=\frac{-50}{-10}
=+5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(30)+20}{2*-5}=\frac{-10}{-10}
=1
$