80000=-15x+1.25x^2

Solution for 80000=-15x+1.25x^2 equation:

80000=-15x+1.25x^2

We move all terms to the left:

80000-(-15x+1.25x^2)=0

We get rid of parentheses

-1.25x^2+15x+80000=0

a = -1.25; b = 15; c = +80000;
Δ = b2-4ac
Δ = 152-4·(-1.25)·80000
Δ = 400225
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:

$\sqrt{\Delta}=\sqrt{400225}=\sqrt{25*16009}=\sqrt{25}*\sqrt{16009}=5\sqrt{16009}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(15)-5\sqrt{16009}}{2*-1.25}=\frac{-15-5\sqrt{16009}}{-2.5}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(15)+5\sqrt{16009}}{2*-1.25}=\frac{-15+5\sqrt{16009}}{-2.5}
$