9900=x^2-15x+56

Solution for 9900=x^2-15x+56 equation:

9900=x^2-15x+56

We move all terms to the left:

9900-(x^2-15x+56)=0

We get rid of parentheses

-x^2+15x-56+9900=0

We add all the numbers together, and all the variables

-1x^2+15x+9844=0

a = -1; b = 15; c = +9844;
Δ = b2-4ac
Δ = 152-4·(-1)·9844
Δ = 39601
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{39601}=199$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(15)-199}{2*-1}=\frac{-214}{-2}
=+107
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(15)+199}{2*-1}=\frac{184}{-2}
=-92
$