30=256b-b^2

Solution for 30=256b-b^2 equation:

30=256b-b^2

We move all terms to the left:

30-(256b-b^2)=0

We get rid of parentheses

b^2-256b+30=0

a = 1; b = -256; c = +30;
Δ = b2-4ac
Δ = -2562-4·1·30
Δ = 65416
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{65416}=\sqrt{4*16354}=\sqrt{4}*\sqrt{16354}=2\sqrt{16354}$
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-256)-2\sqrt{16354}}{2*1}=\frac{256-2\sqrt{16354}}{2}
$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-256)+2\sqrt{16354}}{2*1}=\frac{256+2\sqrt{16354}}{2}
$