H=1.4+30t-4.9t^2

Solution for H=1.4+30t-4.9t^2 equation:

=1.4+30H-4.9H^2

We move all terms to the left:

-(1.4+30H-4.9H^2)=0

We get rid of parentheses

4.9H^2-30H-1.4=0

a = 4.9; b = -30; c = -1.4;
Δ = b2-4ac
Δ = -302-4·4.9·(-1.4)
Δ = 927.44
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$H_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$H_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$H_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-30)-\sqrt{927.44}}{2*4.9}=\frac{30-\sqrt{927.44}}{9.8}
$
$H_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-30)+\sqrt{927.44}}{2*4.9}=\frac{30+\sqrt{927.44}}{9.8}
$