please assist me in understanding this

Exercise 14-36 Algo The maintenance manager at a trucking company wants to build a regression model to forecast the time (in years) until the first engine overhaul based on four explanatory variables: (1) annual miles driven (in 1,000s of miles), (2) average load weight (in tons), (3) average Time Until First Annual Average Engine Overhaul Average Oil Change driving speed (in mph), and (4) oil change interval (in 1,000s of miles). Based on driver logs and onboard computers, data have been Miles Driven Load Weight Driving Speed Interval tained for a sample of 25 trucks. A portion of the data is shown in the accompanying table. 7.9 43.1 21 21 13 Time until First Annual Miles Driven Average Load Average Driving 0.8 Oil Change 98.6 25 25 30 Engine Overhaul 8. 5 7.9 Weight Speed 13.4 43.1 1. Interval 26 26 16 0. 98.6 47.0 25.0 13.0 49.0 30.0 1.2 111.2 25 25 23 6.3 61.2 24. 62.0 1.6 102 23.0 32 32 22 2. 1 96.6 19 19 20 Click here for the Excel Data File 2.1 92.9 21 21 17 7.2 54.3 17 17 16 a. For each explanatory variable, discuss whether it is likely to have a positive or negative causal effect on time until the first engine 8 overhaul. 51.2 24 24 14 4.1 84.8 20 20 27 Explanatory variable Effect on time 0.7 120.6 27 27 24 Annual Miles Driven 5.1 78 28 28 26 Average Load Weight 5.5 68.3 24 24 29 Average Driving Speed 5,3 54.8 19 19 27 Oil Change Interval 5.9 67.2 23 23 22 8.5 38.9 18 18 18 5 .5 52.2 18 18 24 6.2 54 17 17 20 4.7 74.6 18 18 21 6.4 58.7 16 16 21 6.4 52.1 19 19 14 7.2 68.4 22 22 16 4.3 95 21 21 25 7.1 45.4 20 20 15 6.3 61.2 24 24 23 b. Estimate the regression model. (Negative values should be indicated by a minus sign. Round your answers to 4 decimal places.) Time - + Miles + Load + speed + oil c. Based on part (a), are the signs of the regression coefficients logical? Regression coefficients Signs Annual Miles Driven Average Load Weight Average Driving Speed Oil Change Interval