7d-4d(5d+4)=-18

Solution for 7d-4d(5d+4)=-18 equation:

7d-4d(5d+4)=-18

We move all terms to the left:

7d-4d(5d+4)-(-18)=0

We add all the numbers together, and all the variables

7d-4d(5d+4)+18=0

We multiply parentheses

-20d^2+7d-16d+18=0

We add all the numbers together, and all the variables

-20d^2-9d+18=0

a = -20; b = -9; c = +18;
Δ = b2-4ac
Δ = -92-4·(-20)·18
Δ = 1521
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1521}=39$
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-9)-39}{2*-20}=\frac{-30}{-40}
=3/4
$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-9)+39}{2*-20}=\frac{48}{-40}
=-1+1/5
$