A map is drawn to scale such that 1 inch equals 100 miles. To mark a distance of 500 miles, the length on the map must be inches.

Sanya noticed that the temperature was falling at a steady rate of 1.4 degrees every hour from the time that she first checked her outdoor thermometer. by 6 a.m., the temperature had fallen 21 degrees. which expression can you use to find how many hours earlier she had first checked the thermometer?