The post office uses a multiple channel queue, where customers wait in a single line for the first available window. If the average service time is 1 minute and the arrival rate is 7 customers every five minutes, find when two service windows are open

Petra contracted to paint bret’s house for $2,000. after beginning the job, petra realizes that the house is really quite big, and she’s not going to make enough profit, so she tells bret she wants another $500 to finish the job. bret doesn’t want to pay more, but he’s afraid that if she walks off the job, he’ll have trouble finding someone else to finish it, so he agrees. is bret legally obligated to pay the extra $500?