5 : 22.17. A flagpole is n feet tall. On this pole we display flags of the following types: red flags that are 1 foot tall, blue flags that are 2 feet tall, and green flags that are 2 feet tall. The sum of the heights of the flags is exactly n feet. Prove that there are 2 3 2 n C 1 3 .1/n ways to disp