0=100t-4.9t^2

Solution for 0=100t-4.9t^2 equation:

0=100t-4.9t^2

We move all terms to the left:

0-(100t-4.9t^2)=0

We add all the numbers together, and all the variables

-(100t-4.9t^2)=0

We get rid of parentheses

4.9t^2-100t=0

a = 4.9; b = -100; c = 0;
Δ = b2-4ac
Δ = -1002-4·4.9·0
Δ = 10000
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{10000}=100$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-100)-100}{2*4.9}=\frac{0}{9.8}
=0
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-100)+100}{2*4.9}=\frac{200}{9.8}
=20+4/9.8
$