20=0,6q^2-8q

Solution for 20=0,6q^2-8q equation:

20=0.6q^2-8q

We move all terms to the left:

20-(0.6q^2-8q)=0

We get rid of parentheses

-0.6q^2+8q+20=0

a = -0.6; b = 8; c = +20;
Δ = b2-4ac
Δ = 82-4·(-0.6)·20
Δ = 112
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$q_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$q_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{112}=\sqrt{16*7}=\sqrt{16}*\sqrt{7}=4\sqrt{7}$
$q_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(8)-4\sqrt{7}}{2*-0.6}=\frac{-8-4\sqrt{7}}{-1.2}
$
$q_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(8)+4\sqrt{7}}{2*-0.6}=\frac{-8+4\sqrt{7}}{-1.2}
$