A machine requires a constant 40 seconds to insert a part. Parts arrive at the machine for insertion at the rate of 1 part per minute according to a Poisson distribution. The average time (in seconds) a part spends in the system (waiting and being inserted) is
a. 120 seconds
b. 80 seconds
c. 60 seconds
d. 40 seconds
What option is it a,b,c, or d?