The simple equations in the first problem ignore the effects of variables other than the price on supply and demand. More complete represen- tations of supply and demand curves might include additional variables other than just the price. Suppose that the supply of wheat depends on the price of wheat (p) and the amount of rainfall (r). The demand for wheat depends on the price of wheat and the level of disposable income (I). The equations describing the supply and demand relationships are: Qs = 20r + 100p QD=4000-100p+101 (a) Sketch a graph of demand and supply curves that shows the effect of an increase in rainfall. How does each of the curves shift (if at all) from the increase? What is the effect on equilibrium price and quantity? (b) Sketch a graph of demand and supply curves that shows the effect of an increase in disposable income. How does each of the curves shift (if at all) from the increase? What is the effect on equilibrium price and quantity? (c) Now you are to confirm your graphs with algebra. Solve the supply and demand equations for the equilibrium price and quantity, Q* and p" as a function of the exogenous variables I and r. (d) Explain how the variables I and r affect the equilibrium price accord- ing to your answers to (c). Does it conform to the graphical analysis in part (a)?