If c is a number with no exponent, what is the value of c in the equation below? 4^7/4^3=a^b=c

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?