You have a research project due in four weeks and each week you have a party invitation. But to finish

the project you need to skip just one party. This means you only can attend three parties in four weeks. The payoff,

x$,$ of Party A this week $($t $=0)$ is $9,$ that of Party B in next week $($t $=1)$ is $25,$ that of Party C in two weeks $($t $=2)$ is $64,$

and that of Party D in three weeks $($t $=3)$ is $169.$ As you can see Part D gives you highest payoff.