2.9 Nataraj (2007) found that a 100% increase in the price of water for heavy users in Santa Cruz, California, caused the quantity of water they demanded to fall by an average of 20%. (Before the increase, heavy users initially paid $1.55 per unit, but afterward they paid $3.14 per unit.) In percentage terms, how much did their water expenditure (price times quantity)—which is the water company’s revenue—change? (Hint: See Solved Problem 3.2.)