20=15.04x+4.9x^2

Solution for 20=15.04x+4.9x^2 equation:

20=15.04x+4.9x^2

We move all terms to the left:

20-(15.04x+4.9x^2)=0

We get rid of parentheses

-4.9x^2-15.04x+20=0

a = -4.9; b = -15.04; c = +20;
Δ = b2-4ac
Δ = -15.042-4·(-4.9)·20
Δ = 618.2016
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15.04)-\sqrt{618.2016}}{2*-4.9}=\frac{15.04-\sqrt{618.2016}}{-9.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15.04)+\sqrt{618.2016}}{2*-4.9}=\frac{15.04+\sqrt{618.2016}}{-9.8}
$