x+x(18/100)=100

Solution for x+x(18/100)=100 equation:

x+x(18/100)=100

We move all terms to the left:

x+x(18/100)-(100)=0

We add all the numbers together, and all the variables

x+x(+18/100)-100=0

We multiply parentheses

18x^2+x-100=0

a = 18; b = 1; c = -100;
Δ = b2-4ac
Δ = 12-4·18·(-100)
Δ = 7201
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)-\sqrt{7201}}{2*18}=\frac{-1-\sqrt{7201}}{36}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1)+\sqrt{7201}}{2*18}=\frac{-1+\sqrt{7201}}{36}
$