If the Marginal Utilities Are Constant for Travel and Food

Multiple Choice

If the marginal utilities are constant for travel and food and the marginal utility per dollar of travel is 50 and the marginal utility per dollar of food is 30:

A) the total utility of food and travel is 80.
B) we can gain 20 units of net utility by spending one less dollar on food and one more dollar on travel.
C) we can gain 20 units of net utility by spending one more dollar on food and one less dollar on travel.
D) we can gain 30 units of net utility by spending one less dollar on food and one more dollar on travel.