B=0.8d^2-2.4d

Solution for B=0.8d^2-2.4d equation:

=0.8B^2-2.4B

We move all terms to the left:

-(0.8B^2-2.4B)=0

We get rid of parentheses

-0.8B^2+2.4B=0

a = -0.8; b = 2.4; c = 0;
Δ = b2-4ac
Δ = 2.42-4·(-0.8)·0
Δ = 5.76
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$B_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$B_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$B_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(2.4)-\sqrt{5.76}}{2*-0.8}=\frac{-2.4-\sqrt{5.76}}{-1.6}
$
$B_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(2.4)+\sqrt{5.76}}{2*-0.8}=\frac{-2.4+\sqrt{5.76}}{-1.6}
$