Please help me on this problem

Little’s law firm has just one lawyer. customers arrive randomly at an average rate of 6 per 8 hour workday. service times have a mean of 50 minutes and a standard deviation of 20 minutes. how long does a customer spend at little’s law firm on average?

See attachment below and find the equivalent of tan(∠qsr)

Solve the following pair of equations for x and y: ax/b_ by /a= a +b; ax - by = 2ab