b. A one-tail test can be used for each of the variables. The use of a two-tail test would not change any of the findings. The t test indicates that the impact of the competitor’s price on the product in question is not statistically significant.
c. Interest rates might well have an impact on sales. However, it would be more appropriate in a time-series analysis of sales. The price relative to performance (e.g., price per MIP) might also be an important variable. However, it too would be more appropriate in a time series analysis. And unlike the case of interest rates, the time series data on this variable might not be available simply because the workstation is a relatively new product.