The manager of Hudson Auto Repair wants to advertise one price for an engine tune-up, with parts included. Before he decides the price to advertise, he needs a good estimate of the average cost of tune-up parts. A sample of 26 customer invoices for tune-ups has been selected and the average costs of parts is 81.33. The population standard deviation is 15.41. Calculate the margin of error for a 90% confidence inte rval. (answer upto 2 decimal places)