(8c-7)-(6c-3);c=-9

Solution for (8c-7)-(6c-3);c=-9 equation:

(8c-7)-(6c-3)c=-9

We move all terms to the left:

(8c-7)-(6c-3)c-(-9)=0

We add all the numbers together, and all the variables

(8c-7)-(6c-3)c+9=0

We multiply parentheses

-6c^2+(8c-7)+3c+9=0

We get rid of parentheses

-6c^2+8c+3c-7+9=0

We add all the numbers together, and all the variables

-6c^2+11c+2=0

a = -6; b = 11; c = +2;
Δ = b2-4ac
Δ = 112-4·(-6)·2
Δ = 169
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$c_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$c_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{169}=13$
$c_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(11)-13}{2*-6}=\frac{-24}{-12}
=+2
$
$c_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(11)+13}{2*-6}=\frac{2}{-12}
=-1/6
$