The coefficients of repairs are in reference to repair rating 5. So the cars with repair rating 1 yields about 6.36 less mpg than the cars with repair rating 5, repair rating 2 yields about 8.23 less mpg than repair rating 5, and so on. It makes sense that cars with better repair rating use less gas: they must be constructed to be more efficient. Each dummy is 0 or 1, so to compute the predicted mpg, you can plug in 1 to the rating you want to get an estimation for, and 0 for others. When a car has a repair rating 5, the predicted mpg is 27.36. When a car has a repair rating 1, the predicted mpg is 27.36-6.36 = 21.