0=4.8t-0.39t^2

Solution for 0=4.8t-0.39t^2 equation:

0=4.8t-0.39t^2

We move all terms to the left:

0-(4.8t-0.39t^2)=0

We add all the numbers together, and all the variables

-(4.8t-0.39t^2)=0

We get rid of parentheses

0.39t^2-4.8t=0

a = 0.39; b = -4.8; c = 0;
Δ = b2-4ac
Δ = -4.82-4·0.39·0
Δ = 23.04
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{-(-4.8)-\sqrt{23.04}}{2*0.39}=\frac{4.8-\sqrt{23.04}}{0.78}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-4.8)+\sqrt{23.04}}{2*0.39}=\frac{4.8+\sqrt{23.04}}{0.78}
$