Carina buys two goods, food F and clothing C, with the utility function U = FC + F. Her marginal utility of food is MUF = C + 1 and her marginal utility of clothing is MUC = F. She has an income of 20. The price of clothing is 4.

a) Draw Carina's demand for food for prices of food ranging between 1 and 6.

b) Calculate the income and substitution effects on Carina's consumption of food when the price of food rises from 1 to 4, and draw a graph illustrating these effects.