A shop uses 10 identical machines. Each machine breaks down once every 7 hrs on the average. It takes half an hour on the average to repair a broken machine. Both the breakdown and repair processes follow the Poisson distribution. Determine the following:

(a) The number of repairpersons needed such that the average number of broken machines is less than 1.

(b) The number of repairpersons needed so that the expected delay time until repair is started is less than 10 minutes.