Matthew and Susan are both optimizing consumers in the markets for shirts and hats, where they pay $100 for a shirt and $50 for hat. Matthew buys 4 shirts and 16 hats, while Susan buys 6 shirts and 12 hats. From this information, we can infer that Matthew’s marginal rate of substitution is _____ hats per shirt, while Susan’s is _____.

a. 2, 1

b. 2, 2

c. 4, 1

d. 4, 2