A single channel queue forms at the entrance to an off-street parking area. Arrivals are random, at an average rate of 12 vehicles per minute, and the time required for the service process of removing the time-card from the control box and driving past the boom gate is also random and averages 4 seconds per vehicle. To avoid spillback of the road, the entrance to the off-street parking area was designed to cater for a maximum of 10 vehicles (i.e. including both waiting and being served ). Which option below best represents the chance of spillback occurring?