Andrea has a budget of 21 to spend on toothbrushes and tooth paste. He does not receive any utility from owning a toothbrush, but for the consumption of every tube of tooth paste he gains a utility of 2 utils but only if he owns a tooth brush. Without a tooth brush, Andrea gains m utility from consuming tooth paste. In addition, after consuming 10 tubes of tooth paste, a toothbrush needs to be replaced, i.e., Andrea needs to buy a new one. The current price of tooth brushes on the market is 5 and the current price for tooth paste is 1 per tube. Assume that Andrea aims to maximise consumer surplus. a) How many tubes will Andrea buy if he wants to maximise consumer surplus, assuming that Andrea can buy any amount of tooth brushes? What is Andrea's total consumer surpius? Find Andrea's income-consumption curve for tooth paste tubes for incomes between 0 and 21, assuming a price of 1 per tube