0=0.8-1.2t-0.6t^2

Solution for 0=0.8-1.2t-0.6t^2 equation:

0=0.8-1.2t-0.6t^2

We move all terms to the left:

0-(0.8-1.2t-0.6t^2)=0

We add all the numbers together, and all the variables

-(0.8-1.2t-0.6t^2)=0

We get rid of parentheses

0.6t^2+1.2t-0.8=0

a = 0.6; b = 1.2; c = -0.8;
Δ = b2-4ac
Δ = 1.22-4·0.6·(-0.8)
Δ = 3.36
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{-(1.2)-\sqrt{3.36}}{2*0.6}=\frac{-1.2-\sqrt{3.36}}{1.2}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1.2)+\sqrt{3.36}}{2*0.6}=\frac{-1.2+\sqrt{3.36}}{1.2}
$