Someone answer the blank please :/

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

According to the 2008 u.s. census, california had a population of approximately 4 × 10^7 people and florida had a population of approximately 2 × 10^7 people. which of the following is true? a. the population of california was approximately two times the population of florida. b. the population of florida was approximately twenty times the population of california. c. the population of florida was approximately two times the population of california. d. the population of california was approximately twenty times the population of florida.

1.based of the diagrams what is the the value of x? 2.how would you verify your answer for x