The answer is 15
From the graph:
Car A traveled 60 miles in one hour
Car B traveled 75 miles in one hour.
Car B travels 15 more miles per hour
A proportional graph is a straight line that goes through the origin while a non-proportional graph is a straight line that doesn't go through the origin.
y = mx + b
the b represents the y-intercept, so -3 is the y-intercept in the equation y = 3x -3
therefore, the line doesn't go through the origin and is a non-proportional equation
