A researcher compares the effectiveness of two different instructional methods for teaching physiology. A sample of 155 students using Method 1 produces a testing average of 62.7. A sample of 130 students using Method 2 produces a testing average of 89.5. Assume the standard deviation is known to be 16.79 for Method 1 and 14.88 for Method 2. Determine the 90% confidence interval for the true difference between testing averages for students using Method 1 and students using Method 2. Step 1 of 2: Find the critical value that should be used in constructing the confidence interval.