Revise multiplying and dividing integers and multiplying out brackets.

A positive number divided by a negative number results in a negative number.

$$18 \div (-9) = -2$$

The answer is $\boxed{\text{-2}}$.

: Multiplying Out Brackets

3.1 $3(x+y)$

$$3(x+y) = 3 \times x + 3 \times y$$ $$3(x+y) = 3x + 3y$$

The answer is $\boxed{3x+3y}$.