Answer:
The average number of customers in the system is 1.33 customers (option D).
Step-by-step explanation:
This is a problem of queing theory (single-server waiting line).
We have that the arrival rate is [tex]\lambda=4[/tex] and the service rate is [tex]\mu=7[/tex].
The formula for the average number of customers in the system is:
[tex]L=\frac{\lambda}{\mu-\lambda}=\frac{4}{7-4}=\frac{4}{3}=1.33[/tex]