Brandi read a total of 9 books over 3 months. If Brandi has read 12 books so far, how many months has she been with her book club? Assume the relationship is directly proportional.
Set up a proportion and solve for n.

9n 
= 
12 × 3 
Find the cross products 

9n 
= 
36 
Multiply 

n 
= 
4 
Divide both sides by 9 
If Brandi has read 12 books so far, then she has been with her book club for 4 months.