I need to describe the type of mapping in each direction. To determine in which direction (if any) is a function. And if it is a function, to state the domain. Please help this is mapping and functions. I need your help urgently. Thank you.

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?