300=5x^2+55x

Solution for 300=5x^2+55x equation:

300=5x^2+55x

We move all terms to the left:

300-(5x^2+55x)=0

We get rid of parentheses

-5x^2-55x+300=0

a = -5; b = -55; c = +300;
Δ = b2-4ac
Δ = -552-4·(-5)·300
Δ = 9025
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{9025}=95$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-55)-95}{2*-5}=\frac{-40}{-10}
=+4
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-55)+95}{2*-5}=\frac{150}{-10}
=-15
$