A small company is building an electric surveillance device for the government. Each unit must transmit for 25 minutes after being submerged in 10 feet of water for 10 minutes. The company has selected 15 of these units at random. For the sample, the average length of time the units transmitted was 23.3 minutes with a standard deviation of 5.2 minutes. Your sample was normal. You want to be 95 % confident. That is, you will accept a 5% level of significance. What is the standard error of the mean