trying to figure out this problem

John only likes dr. pepper and pizza (and no other goods). At his current level of consumption, he is consuming 2 dr. pepper and 2 pizzas per day. Dr. pepper costs $2, and each pizza costs $10. His daily budget is $24. His marginal utility from dr. pepper is 4. If David is currently maximizing his utility, what is his marginal utility from pizza? Show or explain how you got your