-300=20x-4.9x^2

Solution for -300=20x-4.9x^2 equation:

-300=20x-4.9x^2

We move all terms to the left:

-300-(20x-4.9x^2)=0

We get rid of parentheses

4.9x^2-20x-300=0

a = 4.9; b = -20; c = -300;
Δ = b2-4ac
Δ = -202-4·4.9·(-300)
Δ = 6280
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{6280}=\sqrt{4*1570}=\sqrt{4}*\sqrt{1570}=2\sqrt{1570}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-2\sqrt{1570}}{2*4.9}=\frac{20-2\sqrt{1570}}{9.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+2\sqrt{1570}}{2*4.9}=\frac{20+2\sqrt{1570}}{9.8}
$