The graph below shows the distance, y, that a car traveled in x hours:

a graph is shown with x axis title as time in hours. the title on the y axis is distance traveled in miles. the values on the x axis are from 0 to 5 in increments of 1 for each grid line. the values on the y axis are from 0 to 125 in increments of 25 for each grid line. a line is shown connecting ordered pairs 1, 25 and 2, 50 and 3, 75 and 4, 100. the title of the graph is rate of travel.

what is the rate of change for the relationship represented in the graph?