The equation d = 65t means that the rate is r = 65. So Malcolm's family travels at an average rate of 65 mph. Note this is the slope of the line.
The graph has a slope of 50 because each time we go up 50, we move to the right 1. Ie, slope = rise/run = 50/1 = 50. You could use the slope formula to get the same result.
Since the graph has a slope of 50, this means Theo's family is going at an average speed of 50 mph.
74 is the amount per hour, so you would need to multiply that by the number of hours they work (74t) and the 65 is a set fee (does not change based on the amount of service) so you just add that on
