0=-4.9t^2+21.5t+4

Solution for 0=-4.9t^2+21.5t+4 equation:

0=-4.9t^2+21.5t+4

We move all terms to the left:

0-(-4.9t^2+21.5t+4)=0

We add all the numbers together, and all the variables

-(-4.9t^2+21.5t+4)=0

We get rid of parentheses

4.9t^2-21.5t-4=0

a = 4.9; b = -21.5; c = -4;
Δ = b2-4ac
Δ = -21.52-4·4.9·(-4)
Δ = 540.65
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{-(-21.5)-\sqrt{540.65}}{2*4.9}=\frac{21.5-\sqrt{540.65}}{9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21.5)+\sqrt{540.65}}{2*4.9}=\frac{21.5+\sqrt{540.65}}{9.8}
$