18=7r+r^2

Solution for 18=7r+r^2 equation:

18=7r+r^2

We move all terms to the left:

18-(7r+r^2)=0

We get rid of parentheses

-r^2-7r+18=0

We add all the numbers together, and all the variables

-1r^2-7r+18=0

a = -1; b = -7; c = +18;
Δ = b2-4ac
Δ = -72-4·(-1)·18
Δ = 121
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{121}=11$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-7)-11}{2*-1}=\frac{-4}{-2}
=+2
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-7)+11}{2*-1}=\frac{18}{-2}
=-9
$