Question 9 1 pts Charlie's utility function is XAXB. The price of apple used to be $1. the price of banana used to be $2, and his income used to be $40. If the price of apple increased to $4 and the price of banana stayed constant, the substitution effect on Charlie's apple consumption would reduce his consumption by O 15 apples. 0 3 apples. 0 7.50 apples. 0 12.50 apples