18=5x^2-9x

Solution for 18=5x^2-9x equation:

18=5x^2-9x

We move all terms to the left:

18-(5x^2-9x)=0

We get rid of parentheses

-5x^2+9x+18=0

a = -5; b = 9; c = +18;
Δ = b2-4ac
Δ = 92-4·(-5)·18
Δ = 441
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{441}=21$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(9)-21}{2*-5}=\frac{-30}{-10}
=+3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(9)+21}{2*-5}=\frac{12}{-10}
=-1+1/5
$