Sam is at the garden center and wants to buy a tree, shrug, and a set of perennial flowers. Since it is at the end of the season, the store does not have a lot to choose from. There were only 4 kinds

Sam is at the garden center and wants to buy a tree, shrug, and a set of perennial flowers. Since it is at the end of the season, the store does not have a lot to choose from. There were only 4 kinds of trees and 6 kinds of shrubs. How many different perennial flowers are there if Sam has a total of 168 choices?

A.) 6

B.) 7

C.) 36

D.) 158