Before we calculate we can use some common sence thinknig to narrow down the choices. We know that Robert is gonig DOWN the hill, so it doesnt make sence that he woudl have a positive rate of change (i.e. the number feet up the hill he is is decreasing, not increasing) So right away, A & B are clearly wrong.
If we look at the last two (C & D) we can see that if -460 were right after 10 minutes he would have walked down 4,600 feet. This is WAY more that the total height of the hill and so can't be correct.
So C must be correct.
We can check this with some simple math:
[tex] rate = \frac{end-start}{time} = \frac{0ft-1380ft}{30mins}= -46\frac{ft}{min}[/tex]
