Help i need to finish at a certain time

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.

Assume that y varies inversely with x. if y=1.6 when x=0.5 find x when y=3.2

Need plz been trying to do it for a long time and still haven’t succeeded