Taylor purchased three types of items (bags of candy, picture frames, and some packs of stickers) from a store. The bags of candy are $1, the picture frames are $2, and the packs of stickers are $3. Taylor spent a total of $16 on 9 items, and purchased three times as many bags of candy as she did packs of stickers. How many of each item did she purchase?

If x = the number of bags of candy, y = the number of picture frames, and z = the number of packs of stickers, which equation is not needed to model this situation?
A) x = 3z
B) z = 3x
C) z = x3
D) x + y + z = 9