Notice that the slope of the budget constraint equals the relative price of the two goods—the price of one good compared to the price of the other. A pizza costs 5 times as much as a pint of Pepsi, so the opportunity cost of a pizza is 5 pints of Pepsi. The budget constraint’s slope of 5 reflects the tradeoff the market is offering the consumer: 1 pizza for 5 pints of Pepsi.