Answer:
[tex]r=-18[/tex]
Step-by-step explanation:
1) Combine like terms
[tex]18r-10r-20r+2r+9r=18\\-r=18[/tex]
2) Divide both sides of the equation by the same term
[tex]-r=18\\\frac{-r}{-1} =\frac{18}{-1}[/tex]
3) Simplify
a. Cancel terms that are in both the numerator and denominator
[tex]\frac{-r}{-1} =\frac{18}{-1} \\r=\frac{18}{-1}[/tex]
b. Divide the numbers
[tex]r=-18[/tex]
