0=-4.9t^2+30t+100

Solution for 0=-4.9t^2+30t+100 equation:

0=-4.9t^2+30t+100

We move all terms to the left:

0-(-4.9t^2+30t+100)=0

We add all the numbers together, and all the variables

-(-4.9t^2+30t+100)=0

We get rid of parentheses

4.9t^2-30t-100=0

a = 4.9; b = -30; c = -100;
Δ = b2-4ac
Δ = -302-4·4.9·(-100)
Δ = 2860
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:

$\sqrt{\Delta}=\sqrt{2860}=\sqrt{4*715}=\sqrt{4}*\sqrt{715}=2\sqrt{715}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-30)-2\sqrt{715}}{2*4.9}=\frac{30-2\sqrt{715}}{9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-30)+2\sqrt{715}}{2*4.9}=\frac{30+2\sqrt{715}}{9.8}
$