Does anybody know this? I need some 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.

Type the correct answer in each box. use numerals instead of words. if necessary, use / for the fraction bar. consider the given table.

Given the equation f(x)=a(b)x where the initial value is 40 and the growth rate is 20% what is f(4)