0=-0.02d2+2.6d-66.5,

Solution for 0=-0.02d2+2.6d-66.5, equation:

0=-0.02d^2+2.6d-66.5.

We move all terms to the left:

0-(-0.02d^2+2.6d-66.5.)=0

We add all the numbers together, and all the variables

-(-0.02d^2+2.6d-66.5.)=0

We get rid of parentheses

0.02d^2-2.6d+66.5.=0

We add all the numbers together, and all the variables

0.02d^2-2.6d=0

a = 0.02; b = -2.6; c = 0;
Δ = b2-4ac
Δ = -2.62-4·0.02·0
Δ = 6.76
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{-(-2.6)-\sqrt{6.76}}{2*0.02}=\frac{2.6-\sqrt{6.76}}{0.04}
$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2.6)+\sqrt{6.76}}{2*0.02}=\frac{2.6+\sqrt{6.76}}{0.04}
$