28=0.3r^2

Solution for 28=0.3r^2 equation:

28=0.3r^2

We move all terms to the left:

28-(0.3r^2)=0

We get rid of parentheses

-0.3r^2+28=0

a = -0.3; b = 0; c = +28;
Δ = b2-4ac
Δ = 02-4·(-0.3)·28
Δ = 33.6
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-\sqrt{33.6}}{2*-0.3}=\frac{0-\sqrt{33.6}}{-0.6}
=-\frac{\sqrt{}}{-0.6}
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+\sqrt{33.6}}{2*-0.3}=\frac{0+\sqrt{33.6}}{-0.6}
=\frac{\sqrt{}}{-0.6}
$