Find the value of X in the diagram above

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

Okay so i didn't get this problem petro bought 8 tickets to a basketball game he paid a total of $200 write an equation to determine whether each ticket cost $26 or $28 so i didn't get this question so yeahyou have a good day.

If you could answer these your a life saver