200=-16t^2+140t

Solution for 200=-16t^2+140t equation:

200=-16t^2+140t

We move all terms to the left:

200-(-16t^2+140t)=0

We get rid of parentheses

16t^2-140t+200=0

a = 16; b = -140; c = +200;
Δ = b2-4ac
Δ = -1402-4·16·200
Δ = 6800
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:

$\sqrt{\Delta}=\sqrt{6800}=\sqrt{400*17}=\sqrt{400}*\sqrt{17}=20\sqrt{17}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-140)-20\sqrt{17}}{2*16}=\frac{140-20\sqrt{17}}{32}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-140)+20\sqrt{17}}{2*16}=\frac{140+20\sqrt{17}}{32}
$