George Costanza, a typical New Yorker, works for Kruger Industrial Smoothing. His favorite snack food is a knish (X₁), a popular New York City treat. He particularly enjoys the knishes sold at Yonah Schimmel Knish Bakery on Houston Street where he can also get his favorite drink, homemade vanilla soda (X₂).

The price of a knish is $4, and the price of a homemade vanilla soda is $3.

Let us suppose George's preference for knishes and vanilla sodas is represented by the utility function: U (X₁, X₂) = 9X₁X₂

George's weekly allowance for knishes and vanilla sodas is $72. He must spend the entire amount each day to buy his knishes and sodas, i.e., he cannot save any of it. Q1: Given his utility function U (X₁, X₂) = 9X₁X₂, which of the following expressions represents the marginal utility of sodas (X2)?

Group of answer choices

a) 9X1

b) 6X2

c) 9X2

d) 6X1

Q2: With the help of your answers to questions 4 and 5, can you identify which of the following expressions represent George's marginal rate of substitution (MRS)?

Group of answer choices

a) X1/X2

b) 2X1/X2

c) X2/X1

d) 2X2/X1