30=21.741t+16.1t^2

Solution for 30=21.741t+16.1t^2 equation:

30=21.741t+16.1t^2

We move all terms to the left:

30-(21.741t+16.1t^2)=0

We get rid of parentheses

-16.1t^2-21.741t+30=0

a = -16.1; b = -21.741; c = +30;
Δ = b2-4ac
Δ = -21.7412-4·(-16.1)·30
Δ = 2404.671081
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{-(-21.741)-\sqrt{2404.671081}}{2*-16.1}=\frac{21.741-\sqrt{2404.671081}}{-32.2}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21.741)+\sqrt{2404.671081}}{2*-16.1}=\frac{21.741+\sqrt{2404.671081}}{-32.2}
$