Table 12-4 the Sentient Car Wash in Luther Knows She Is in Is

Table 12-4
The sentient car wash in Luther knows she is in for a busy day when dawn breaks on a gorgeous spring morning.She is capable of washing a car every four minutes, and by the looks of things, it is reasonable to expect a steady stream of twelve cars per hour arriving.Because she is fully automatic, she knows that the four-minute estimate is accurate and invariant.She values her time at $10 per hour.Yes, it seems low, but as a single bay car wash, there are few other jobs in town she is qualified for.(We won't get into her unsuccessful turn at the beauty salon.) She estimates that customer time can be valued at $15 per hour.
-According to the information provided in Table 12-4, how many minutes per hour will the car wash be idle and able to ponder the meaning of life?

A) 9 minutes
B) 10 minutes
C) 12 minutes
D) 15 minutes