A particular telephone number is used to receive both voice calls and fax messages. Suppose that $25(6$ points$)$ A particular telephone number is used to receive both voice calls and fax messages.

Suppose that $40\%$ of the incoming calls involve fax messages, and consider a sample of $25$

incoming calls. Please, answer the following

$($a$)(3$ points$)$ What is the expected $($average$)$ number of calls among the $25$ that involve a fax

message?

$($b$)(3$ points$)$ What is the variance of the number of calls among the $25$ that involve a fax

message?