A manual (wand) car wash has 10 bays. On a Saturday morning, customers arrive at an average rate of 24/hour (assume Poisson arrivals), and each spends an average of 18 minutes washing their car (assume negative exponential distribution). Assuming that customers wait in a common line for the next available bay, what is the average amount of time (in minutes) that a customer spends from the time they enter the lot until the time they leave? (Round to two decimal places).
a. 3.33 mins
b. 7.85 mins
c. 18.00 mins
d. 19.63 mins