64=64t-t^2

Solution for 64=64t-t^2 equation:

64=64t-t^2

We move all terms to the left:

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

We get rid of parentheses

t^2-64t+64=0

a = 1; b = -64; c = +64;
Δ = b2-4ac
Δ = -642-4·1·64
Δ = 3840
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:

$\sqrt{\Delta}=\sqrt{3840}=\sqrt{256*15}=\sqrt{256}*\sqrt{15}=16\sqrt{15}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-64)-16\sqrt{15}}{2*1}=\frac{64-16\sqrt{15}}{2}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-64)+16\sqrt{15}}{2*1}=\frac{64+16\sqrt{15}}{2}
$