20=-16t^2+100t+70

Solution for 20=-16t^2+100t+70 equation:

20=-16t^2+100t+70

We move all terms to the left:

20-(-16t^2+100t+70)=0

We get rid of parentheses

16t^2-100t-70+20=0

We add all the numbers together, and all the variables

16t^2-100t-50=0

a = 16; b = -100; c = -50;
Δ = b2-4ac
Δ = -1002-4·16·(-50)
Δ = 13200
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:

$\sqrt{\Delta}=\sqrt{13200}=\sqrt{400*33}=\sqrt{400}*\sqrt{33}=20\sqrt{33}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-100)-20\sqrt{33}}{2*16}=\frac{100-20\sqrt{33}}{32}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-100)+20\sqrt{33}}{2*16}=\frac{100+20\sqrt{33}}{32}
$