2700=15x+x^2

Solution for 2700=15x+x^2 equation:

2700=15x+x^2

We move all terms to the left:

2700-(15x+x^2)=0

We get rid of parentheses

-x^2-15x+2700=0

We add all the numbers together, and all the variables

-1x^2-15x+2700=0

a = -1; b = -15; c = +2700;
Δ = b2-4ac
Δ = -152-4·(-1)·2700
Δ = 11025
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{11025}=105$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-105}{2*-1}=\frac{-90}{-2}
=+45
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+105}{2*-1}=\frac{120}{-2}
=-60
$