156=-4c+c^2

Solution for 156=-4c+c^2 equation:

156=-4c+c^2

We move all terms to the left:

156-(-4c+c^2)=0

We get rid of parentheses

-c^2+4c+156=0

We add all the numbers together, and all the variables

-1c^2+4c+156=0

a = -1; b = 4; c = +156;
Δ = b2-4ac
Δ = 42-4·(-1)·156
Δ = 640
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$c_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$c_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{640}=\sqrt{64*10}=\sqrt{64}*\sqrt{10}=8\sqrt{10}$
$c_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(4)-8\sqrt{10}}{2*-1}=\frac{-4-8\sqrt{10}}{-2}
$
$c_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(4)+8\sqrt{10}}{2*-1}=\frac{-4+8\sqrt{10}}{-2}
$