Question

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Answer 1

Rate is the same thing as gradient so to work out the gradient you need to use the formula

change in y / change in x

Change in y = y2 - y1

Pick any two points on the graph

Change in y = 30 - 15

Change in y = 15

Change in x = x2 - x1

Change in x = 2 - 1

Change in x = 1

15/1

= 15 dollars per day.

We can double check this by seeing the increase of money per day, for example, here from day two to day three, the money needed increases by 15, so our answer is correct.