equation for the following problem and solve.

It's Monday and you've been asked to recruit some of your friends to help an elderly couple move next Monday, first thing in the morning. You decide it will be easier for you to ask two people to help, then have each of them ask two people to help, and then have those people each ask two people to help, and so on. If a new set of friends is asked to help each day, how many people were asked to help on the fifth day?