If Jill needed to buy 9 bottles of soda for a party in which 12 people attended, how many bottles of soda will she need to buy for a party in which 8 people are attending?

6

Explanation

We can call the number of soda bottles Jill needs to buy for a party in which 8 people are attending is "X"
Cross-multiply to solve a proportion:
(9)(8)=(12)(x)
72=12x
6=x.