(2s)(7s-18)=90

Solution for (2s)(7s-18)=90 equation:

(2s)(7s-18)=90

We move all terms to the left:

(2s)(7s-18)-(90)=0

We multiply parentheses

14s^2-36s-90=0

a = 14; b = -36; c = -90;
Δ = b2-4ac
Δ = -362-4·14·(-90)
Δ = 6336
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$s_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$s_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{6336}=\sqrt{576*11}=\sqrt{576}*\sqrt{11}=24\sqrt{11}$
$s_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-36)-24\sqrt{11}}{2*14}=\frac{36-24\sqrt{11}}{28}
$
$s_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-36)+24\sqrt{11}}{2*14}=\frac{36+24\sqrt{11}}{28}
$