0=4.9t^2+7.9t-6.336

Solution for 0=4.9t^2+7.9t-6.336 equation:

0=4.9t^2+7.9t-6.336

We move all terms to the left:

0-(4.9t^2+7.9t-6.336)=0

We add all the numbers together, and all the variables

-(4.9t^2+7.9t-6.336)=0

We get rid of parentheses

-4.9t^2-7.9t+6.336=0

a = -4.9; b = -7.9; c = +6.336;
Δ = b2-4ac
Δ = -7.92-4·(-4.9)·6.336
Δ = 186.5956
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-7.9)-\sqrt{186.5956}}{2*-4.9}=\frac{7.9-\sqrt{186.5956}}{-9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-7.9)+\sqrt{186.5956}}{2*-4.9}=\frac{7.9+\sqrt{186.5956}}{-9.8}
$