Bart and Lisa are both optimizing consumers in the markets for shirts and hats, where they pay $100 for a shirt and $50 for a hat. Bart buys 8 shirts and 4 hats, while Lisa buys 6 shirts and 12 hats. From this information, we can infer that Bart’s marginal rate of substitution is _________ hats per shirt, while Lisa’s is _________.

a. 2; 1

b. 2; 2

c. 4; 1

d. 4; 2