Given two goods, X and Y, their prices, PX and PY, and a constant marginal utility of money, a consumer is in equiLiBrium when the last dollar spent on X yields ________.
1) zero marginal utility for Y
2) the same marginal utility as if all the money were spent on Y
3) a smaller marginal utility than the last dollar spent on Y
4) the same marginal utility as the last dollar spent on Y
5) none of the above