Help me please! This is very confusing.

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

Hi, can anyone show me how to do this problem? 100 points for this. in advance

Aparticular telephone number is used to receive both voice calls and fax messages. suppose that 25% of the incoming calls involve fax messages, and consider a sample of 25 incoming calls. (a) what is the expected number of calls among the 25 that involve a fax message?