6400=-16t2+800t

Solution for 6400=-16t2+800t equation:

6400=-16t^2+800t

We move all terms to the left:

6400-(-16t^2+800t)=0

We get rid of parentheses

16t^2-800t+6400=0

a = 16; b = -800; c = +6400;
Δ = b2-4ac
Δ = -8002-4·16·6400
Δ = 230400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{230400}=480$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-800)-480}{2*16}=\frac{320}{32}
=10
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-800)+480}{2*16}=\frac{1280}{32}
=40
$