7=0.013x^2-1.19x+28.24

Solution for 7=0.013x^2-1.19x+28.24 equation:

7=0.013x^2-1.19x+28.24

We move all terms to the left:

7-(0.013x^2-1.19x+28.24)=0

We get rid of parentheses

-0.013x^2+1.19x-28.24+7=0

We add all the numbers together, and all the variables

-0.013x^2+1.19x-21.24=0

a = -0.013; b = 1.19; c = -21.24;
Δ = b2-4ac
Δ = 1.192-4·(-0.013)·(-21.24)
Δ = 0.31162
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{-(1.19)-\sqrt{0.31162}}{2*-0.013}=\frac{-1.19-\sqrt{0.31162}}{-0.026}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1.19)+\sqrt{0.31162}}{2*-0.013}=\frac{-1.19+\sqrt{0.31162}}{-0.026}
$