(d) Find the critical t-value that corresponds to $90 \%$ confidence. Assume 7 degrees of freedom. (Round' to three decimal places as needed.)

Step 1 ：The critical t-value is a point (or points) on the scale of the t-distribution that is used to separate regions of the scale that will lead to the acceptance of a null hypothesis in a t-test from regions that will lead to the rejection of the null hypothesis.

Step 2 ：The critical t-value for a 90% confidence level with 7 degrees of freedom can be found using the t-distribution table or using a statistical function.

Step 3 ：For a two-tailed test at a 90% confidence level, the significance level is 0.10. Therefore, the probability used is 1 - 0.10/2 = 0.95.

Step 4 ：Using these values, we can calculate the critical t-value.

Step 5 ：Final Answer: The critical t-value that corresponds to $90 \%$ confidence with 7 degrees of freedom is \(\boxed{1.895}\).