Calvin and Hobbes by Bill Watterson for October 19, 1989
Calvin: I've got an idea, Dad. Maybe I'd get better grades if you offered me $1 for every "D," $5 for every "C," $10 for every "B," and $50 for every "A"! Dad: I'm not going to bribe you, Calvin. You should apply yourself for your own good. Calvin: Rats. I thought I could make an easy four bucks.