30=30t+4.9t^2

Solution for 30=30t+4.9t^2 equation:

30=30t+4.9t^2

We move all terms to the left:

30-(30t+4.9t^2)=0

We get rid of parentheses

-4.9t^2-30t+30=0

a = -4.9; b = -30; c = +30;
Δ = b2-4ac
Δ = -302-4·(-4.9)·30
Δ = 1488
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:

$\sqrt{\Delta}=\sqrt{1488}=\sqrt{16*93}=\sqrt{16}*\sqrt{93}=4\sqrt{93}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-30)-4\sqrt{93}}{2*-4.9}=\frac{30-4\sqrt{93}}{-9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-30)+4\sqrt{93}}{2*-4.9}=\frac{30+4\sqrt{93}}{-9.8}
$