A buyer's preferences are represented by the following utility function and the corresponding marginal utility functions for each of the two goods in the economy; iTunes songs and beer.

U = 50s?b?

MUs? = 25sb??

MUb? =bs??

Where MUs? is the marginal utility of songs and MUb? is the marginal utility of beer. We also know that the market price of an iTunes song is $1, the price of a beer is $4, and the consumer's budget is $100.