4. You observed a small business's telephone calls over a two-hour period. During that time, 22 calls came in. However, during that same period, the time during which all t

elephone lines were busy was 30 minutes.

a. Determine the maximum-likelihood estimate of the arrival rate. Express your answers in calls per hour, rounded to the nearest tenth of a call.

b. Determine a 90% confidence interval for the true, but unknown, arrival rate, assuming the arrivals have a Poisson distribution. Express the lower and upperlimits in calls per hours, rounded to the nearest tenth of a call.