4=-16x^2+42.2x

Solution for 4=-16x^2+42.2x equation:

4=-16x^2+42.2x

We move all terms to the left:

4-(-16x^2+42.2x)=0

We get rid of parentheses

16x^2-42.2x+4=0

a = 16; b = -42.2; c = +4;
Δ = b2-4ac
Δ = -42.22-4·16·4
Δ = 1524.84
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{-(-42.2)-\sqrt{1524.84}}{2*16}=\frac{42.2-\sqrt{1524.84}}{32}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-42.2)+\sqrt{1524.84}}{2*16}=\frac{42.2+\sqrt{1524.84}}{32}
$