30=0.81t^2

Solution for 30=0.81t^2 equation:

30=0.81t^2

We move all terms to the left:

30-(0.81t^2)=0

We get rid of parentheses

-0.81t^2+30=0

a = -0.81; b = 0; c = +30;
Δ = b2-4ac
Δ = 02-4·(-0.81)·30
Δ = 97.2
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)-\sqrt{97.2}}{2*-0.81}=\frac{0-\sqrt{97.2}}{-1.62}
=-\frac{\sqrt{}}{-1.62}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+\sqrt{97.2}}{2*-0.81}=\frac{0+\sqrt{97.2}}{-1.62}
=\frac{\sqrt{}}{-1.62}
$