Finding the Marginal Cost of Consumption
Five burgers cost $15, leaving $15 to spend on tacos, or 15 tacos.
The marginal utility of 15 tacos is one util.
Given the price of burgers and tacos, there is a tradeoff of 3 tacos per burger.
Marginal cost of a burger = marginal utility of tacos x tradeoff between burgers and tacos.
Marginal cost of fifth burger = 1 util per taco x 3 tacos per burger