part A: I have been pulling my hair out trying to get this part. I just do not see it...

I tried to do the e and f part but I do not understand it eather.

part E: I put the T(x) in my ti-83 for the Y= and then i set my TBLset and then use the table. I do not understand the answer. On my Table when x=20 my Y1 = 1.6853 not the one mile it is asking. Because when x = 25 my table says Y1 = 1.0983 and that seems like it would be closer to one then the answer my books gives.

part F: And how do you do a Minimum on a non - parabola graph. I keep on trying to get but not sure were to look. The book also says that x= 20 miles for this one to.