A manufacturer of cream filled donuts collected data from its automatic filling process. The amount of cream inserted into the donuts is normally distributed. To make sure that the automatic filling process is on target, quality control inspectors take a sample of 25 donuts and measure the weight of cream filling. They find a sample mean weight of 15 grams with a standard deviation of 1. 5 grams. What is the margin of error at 90% confidence?.