Need help don't know what the A means

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?

Yuto solved the equation below. what is the solution to yuto’s equation?

Solve one step and two step problems