Traci Consumes Two Goods,lemonade and Pretzels

Multiple Choice

Traci consumes two goods,lemonade and pretzels.Lemonade costs $2 per glass,and she consumes it to the point where the marginal utility she receives from her last glass of lemonade is 4.Pretzels cost $3 per bag.The relationship between the marginal utility Traci gets from eating a bag of pretzels and the number of bags she eats per month is as follows:
If Traci is maximizing her utility,how many bags of potato chips does she buy each month?

A) 3
B) 4
C) 5
D) 6