-4*k*(5-k)=0

Solution for -4*k*(5-k)=0 equation:

-4k(5-k)=0

We add all the numbers together, and all the variables

-4k(-1k+5)=0

We multiply parentheses

4k^2-20k=0

a = 4; b = -20; c = 0;
Δ = b2-4ac
Δ = -202-4·4·0
Δ = 400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$k_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$k_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{400}=20$
$k_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-20}{2*4}=\frac{0}{8}
=0
$
$k_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+20}{2*4}=\frac{40}{8}
=5
$