Tyrone is an investment broker who tells his clients that some investments are a moderate risk and others are an aggressive risk. He wants to know the difference between the annual return on the investments in each category. He sampled 17 investments from each category. There was a mean annual return of 6.2% on the investments in the moderate sample, with a standard deviation of 9.3%. The aggressive investments had a sample mean of 7.3% and a standard deviation of 12.4%. Assume that the conditions for inference have been met, and that Tyrone will use the conservative degrees of freedom corresponding to a sample size of 17. Leta - Am be the difference in mean annual return (in percents) of the groups of investments. Which of the following is a 90% confidence interval for p - um?