30=4.9t^2

Solution for 30=4.9t^2 equation:

30=4.9t^2

We move all terms to the left:

30-(4.9t^2)=0

We get rid of parentheses

-4.9t^2+30=0

a = -4.9; b = 0; c = +30;
Δ = b2-4ac
Δ = 02-4·(-4.9)·30
Δ = 588
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{588}=\sqrt{196*3}=\sqrt{196}*\sqrt{3}=14\sqrt{3}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-14\sqrt{3}}{2*-4.9}=\frac{0-14\sqrt{3}}{-9.8}
=-\frac{14\sqrt{3}}{-9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+14\sqrt{3}}{2*-4.9}=\frac{0+14\sqrt{3}}{-9.8}
=\frac{14\sqrt{3}}{-9.8}
$