75=13x+4.9x^2

Solution for 75=13x+4.9x^2 equation:

75=13x+4.9x^2

We move all terms to the left:

75-(13x+4.9x^2)=0

We get rid of parentheses

-4.9x^2-13x+75=0

a = -4.9; b = -13; c = +75;
Δ = b2-4ac
Δ = -132-4·(-4.9)·75
Δ = 1639
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{-(-13)-\sqrt{1639}}{2*-4.9}=\frac{13-\sqrt{1639}}{-9.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-13)+\sqrt{1639}}{2*-4.9}=\frac{13+\sqrt{1639}}{-9.8}
$