4 mph is a rate, and is represented by a straight line thru the origin with slope 4/1.
Draw a set of coordinate axes and label them t (for time) and d(for distance).
Start with your pencil point at the origin. Arbitrarily move this point 3 spaces to the right, and from there move it 4 spaces up. You'll be at (3,4).
Draw a straight line from the origin (0,0) to the point (3,4).