If during the last 100 feet of approaching a railroad crossing, you cannot see the track for at least 400 feet in both directions, you may not cross the tracks at a speed faster than mph.

If during the last 100 feet of approaching a railroad crossing, you cannot see the track for at least 400 feet in both directions, you may not cross the tracks at a speed faster than 15 mph.
Because this is the speed that is allowed when a person is not able to see the track for at least 400 feet in both directions.

The answer is C

Explanation:

Law of inertia, also called Newton's first law, postulate in physics that, if a body is at rest or moving at a constant speed in a straight line, it will remain at rest or keep moving in a straight line at constant speed unless it is acted upon by a force.