A maintenance service facility has Poisson arrival rates, negative exponential service time and operates on ‘first come first served’ queue discipline. Breakdowns occur on an average of 3 per day with a range of zero to eight. The maintenance crew can service an average of 6 machines per day with a range of zero to seven. The men waiting time for an item to be serviced would be
(a) 
$\frac{1}{6}$ day (b) $\frac{1}{3}$
day
(c) 1 day (d) 3 days