800=-16t^2+256t

Solution for 800=-16t^2+256t equation:

800=-16t^2+256t

We move all terms to the left:

800-(-16t^2+256t)=0

We get rid of parentheses

16t^2-256t+800=0

a = 16; b = -256; c = +800;
Δ = b2-4ac
Δ = -2562-4·16·800
Δ = 14336
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{14336}=\sqrt{1024*14}=\sqrt{1024}*\sqrt{14}=32\sqrt{14}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-256)-32\sqrt{14}}{2*16}=\frac{256-32\sqrt{14}}{32}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-256)+32\sqrt{14}}{2*16}=\frac{256+32\sqrt{14}}{32}
$