64=16t2-80t

Solution for 64=16t2-80t equation:

64=16t^2-80t

We move all terms to the left:

64-(16t^2-80t)=0

We get rid of parentheses

-16t^2+80t+64=0

a = -16; b = 80; c = +64;
Δ = b2-4ac
Δ = 802-4·(-16)·64
Δ = 10496
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:

$\sqrt{\Delta}=\sqrt{10496}=\sqrt{256*41}=\sqrt{256}*\sqrt{41}=16\sqrt{41}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(80)-16\sqrt{41}}{2*-16}=\frac{-80-16\sqrt{41}}{-32}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(80)+16\sqrt{41}}{2*-16}=\frac{-80+16\sqrt{41}}{-32}
$