Pls answer quick I need help

There were 816 people at a concert when a band started to play. after each song, only half the people stayed to hear the next song. how many people were left at the concert after x songs? write a function to represent this scenario.

If 20% of a number is 35, what is 50% of that number?

Awasher and a dryer cost $701 combined. the washer costs $51 more than the dryer. what is the cost of the dryer?