large sample, confidence interval

Information was collected froma random sample of 20 of the 2000 employees in a factory about the amount of money they were carrying. The mean amount was found to be $5.25 and the estimated standard deviation was £2. On the assumption that the amount of money per person is normally distributed, find a 95% confidence interval for the total amount of money carried by the 2000 emplyees of the factory. The answer somehow is (8630,12370) but I can't quite see how this was achieved. If anyone knows how this was found they'b be a great help. many thanx