Your college newspaper, The Collegiate Investigator, has fixed production costs of $72 per edition and marginal printing and distribution costs of 40¢ per copy. The Collegiate Investigator sells for 60¢ per copy.

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?