.8d^2-2.4d=16

Solution for .8d^2-2.4d=16 equation:

.8d^2-2.4d=16

We move all terms to the left:

.8d^2-2.4d-(16)=0

a = .8; b = -2.4; c = -16;
Δ = b2-4ac
Δ = -2.42-4·.8·(-16)
Δ = 56.96
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-2.4)-\sqrt{56.96}}{2*.8}=\frac{2.4-\sqrt{56.96}}{1.6}
$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2.4)+\sqrt{56.96}}{2*.8}=\frac{2.4+\sqrt{56.96}}{1.6}
$