900=160h^2-60h+420

Solution for 900=160h^2-60h+420 equation:

900=160h^2-60h+420

We move all terms to the left:

900-(160h^2-60h+420)=0

We get rid of parentheses

-160h^2+60h-420+900=0

We add all the numbers together, and all the variables

-160h^2+60h+480=0

a = -160; b = 60; c = +480;
Δ = b2-4ac
Δ = 602-4·(-160)·480
Δ = 310800
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$h_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$h_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{310800}=\sqrt{400*777}=\sqrt{400}*\sqrt{777}=20\sqrt{777}$
$h_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(60)-20\sqrt{777}}{2*-160}=\frac{-60-20\sqrt{777}}{-320}
$
$h_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(60)+20\sqrt{777}}{2*-160}=\frac{-60+20\sqrt{777}}{-320}
$