8=15x-4.9x^2

Solution for 8=15x-4.9x^2 equation:

8=15x-4.9x^2

We move all terms to the left:

8-(15x-4.9x^2)=0

We get rid of parentheses

4.9x^2-15x+8=0

a = 4.9; b = -15; c = +8;
Δ = b2-4ac
Δ = -152-4·4.9·8
Δ = 68.2
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{-(-15)-\sqrt{68.2}}{2*4.9}=\frac{15-\sqrt{68.2}}{9.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+\sqrt{68.2}}{2*4.9}=\frac{15+\sqrt{68.2}}{9.8}
$