x+x+x(x+18)+(x+18)=76

Solution for x+x+x(x+18)+(x+18)=76 equation:

x+x+x(x+18)+(x+18)=76

We move all terms to the left:

x+x+x(x+18)+(x+18)-(76)=0

We add all the numbers together, and all the variables

2x+x(x+18)+(x+18)-76=0

We multiply parentheses

x^2+2x+18x+(x+18)-76=0

We get rid of parentheses

x^2+2x+18x+x+18-76=0

We add all the numbers together, and all the variables

x^2+21x-58=0

a = 1; b = 21; c = -58;
Δ = b2-4ac
Δ = 212-4·1·(-58)
Δ = 673
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{-(21)-\sqrt{673}}{2*1}=\frac{-21-\sqrt{673}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(21)+\sqrt{673}}{2*1}=\frac{-21+\sqrt{673}}{2}
$