Which ones are functions

The sum of two numbers is 12 and their difference is 18 what are the two numbers

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?

Which expression and diagram represent “renee biked four times as far this month as last month”?