C(t)=60-0.75t^2

Solution for C(t)=60-0.75t^2 equation:

(C)=60-0.75C^2

We move all terms to the left:

(C)-(60-0.75C^2)=0

We get rid of parentheses

0.75C^2+C-60=0

a = 0.75; b = 1; c = -60;
Δ = b2-4ac
Δ = 12-4·0.75·(-60)
Δ = 181
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$C_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$C_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$C_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(1)-\sqrt{181}}{2*0.75}=\frac{-1-\sqrt{181}}{1.5}
$
$C_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1)+\sqrt{181}}{2*0.75}=\frac{-1+\sqrt{181}}{1.5}
$