John is running a rabies vaccination clinic for dogs at the local grade school.  John hires a technician who can vaccinate a dog every 3 minutes.  It is estimated that the dogs will arrive independently and randomly throughout the day at a rate of 1 dog every 6 minutes, according to a Poisson distribution.  Also, assume that the vaccinating times are exponentially distributed.  John would like to have each waiting dog placed in a cage.  

a) If John wants to be certain he has enough cages to accommodate all dogs at least 90 percent of the time, how many cages should he prepare?  

b) John considers an option to hire another technician who can work at the same rate as the existing one. The salary for each technician will be 15$ per hour with 8 working hours per day. The waiting cost in line for dog owners is $40/hour. Should John hire another technician?