Itried several attempts to try this problem and i need someone to explain.

A)

For example, for the 400 calories burned he covered 40 minutes, that can be seen from the graph.

The number of minutes per calorie burnt:

=  40 minutes / 400 calories

= 0.1 minute / calorie

So David ran 0.1 minute for each calorie burned.

b)

Slope of the graph formed:

Let us take any two points on the graph are:

The x axis has minutes and the y axis is for the calories.

(0 mins , 0 calories)  and (40 minutes and 400 calories)

Slope = (Change in Calories) / (Change in minutes)

Slope = (400 - 0) calories / (40 - 0 ) minutes

           = 400 calories / 40 minutes

 Slope  = 10 calories/minute

I hope this helps.