y=60+2X-0.5X^2

Solution for y=60+2X-0.5X^2 equation:

y=60+2y-0.5y^2

We move all terms to the left:

y-(60+2y-0.5y^2)=0

We get rid of parentheses

0.5y^2-2y+y-60=0

We add all the numbers together, and all the variables

0.5y^2-1y-60=0

a = 0.5; b = -1; c = -60;
Δ = b2-4ac
Δ = -12-4·0.5·(-60)
Δ = 121
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{121}=11$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-1)-11}{2*0.5}=\frac{-10}{1}
=-10
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+11}{2*0.5}=\frac{12}{1}
=12
$