54. A retail wanted to estimate the monthly fixed and variable selling expenses. As a first step, she collected data form the past 8 months. The total selling expenses ($1,000) and the total sales ($1,000) were recorded and listed below. Total Sales 20 40 60 50 50 55 60 70 Expenses 14 16 18 17 18 18 18 20 Compute the covariance of total sales and expenses. a. 25.2807 b. 25.3807 c. 25.4807 d. 26.1607 e. 26.2807