T(t)=-0.021t^2+0.4536t+98.9.

Solution for T(t)=-0.021t^2+0.4536t+98.9. equation:

(T)=-0.021T^2+0.4536T+98.9.

We move all terms to the left:

(T)-(-0.021T^2+0.4536T+98.9.)=0

We get rid of parentheses

0.021T^2-0.4536T+T-98.9.=0

We add all the numbers together, and all the variables

0.021T^2+0.5464T=0

a = 0.021; b = 0.5464; c = 0;
Δ = b2-4ac
Δ = 0.54642-4·0.021·0
Δ = 0.29855296
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$T_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$T_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$T_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0.5464)-\sqrt{0.29855296}}{2*0.021}=\frac{-0.5464-\sqrt{0.29855296}}{0.042}
$
$T_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0.5464)+\sqrt{0.29855296}}{2*0.021}=\frac{-0.5464+\sqrt{0.29855296}}{0.042}
$