#### Answer

-2r

#### Work Step by Step

The distributive property holds that $a(b+c)=ab+ac$ (for real numbers $a$, $b$, and $c$).
Therefore, $7r-9r=7r+(-9r)=[7+(-9)]r=-2r$.
In this case, we have used the distributive property in reverse to write the given subtraction as a product.