4=6t+4.9t^2

Solution for 4=6t+4.9t^2 equation:

4=6t+4.9t^2

We move all terms to the left:

4-(6t+4.9t^2)=0

We get rid of parentheses

-4.9t^2-6t+4=0

a = -4.9; b = -6; c = +4;
Δ = b2-4ac
Δ = -62-4·(-4.9)·4
Δ = 114.4
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{-(-6)-\sqrt{114.4}}{2*-4.9}=\frac{6-\sqrt{114.4}}{-9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-6)+\sqrt{114.4}}{2*-4.9}=\frac{6+\sqrt{114.4}}{-9.8}
$