(30-y)*y=125

Solution for (30-y)*y=125 equation:

(30-y)*y=125

We move all terms to the left:

(30-y)*y-(125)=0

We add all the numbers together, and all the variables

(-1y+30)*y-125=0

We multiply parentheses

-1y^2+30y-125=0

a = -1; b = 30; c = -125;
Δ = b2-4ac
Δ = 302-4·(-1)·(-125)
Δ = 400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{400}=20$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(30)-20}{2*-1}=\frac{-50}{-2}
=+25
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(30)+20}{2*-1}=\frac{-10}{-2}
=+5
$