4=16x-4.905x^2

Solution for 4=16x-4.905x^2 equation:

4=16x-4.905x^2

We move all terms to the left:

4-(16x-4.905x^2)=0

We get rid of parentheses

4.905x^2-16x+4=0

a = 4.905; b = -16; c = +4;
Δ = b2-4ac
Δ = -162-4·4.905·4
Δ = 177.52
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-16)-\sqrt{177.52}}{2*4.905}=\frac{16-\sqrt{177.52}}{9.81}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-16)+\sqrt{177.52}}{2*4.905}=\frac{16+\sqrt{177.52}}{9.81}
$