Accountants at the Renong and Khalid Accountant Company believed that several traveling executives were submitting unusually high travel vouchers when they returned from business trips. First, they took a sample of 200 vouchers submitted from the past year. Then they developed the following multiple-regression equation relating expected travel cost (Y) to number of days on the road (X₁) and distance traveled (X₂) in miles:

Y = 90.00 + 48.50X₁ + 0.40X₂

Here is additional information concerning the regression model:

Sb₁ = 0.038 Sb₂ =0.019

R² = 0.68 Se = 1.63 F-Statistic = 32.123

Durbin-Watson (d) statistic = 0.5436

a) Which of the independent variables appear to be statistically significant (at the 0.05 significant level) in explaining the expected travel cost for accountants?. Explain.

b) (Mr. Ghazali returns from a 200-mile trip that took him out of town for 5 days), what is the expected amount of his claim.

c) What proportion of the total variation in expected travel cost is explained by the regression equation? Explain.

d) In your opinion, should there any other variables be included? Explain.