Shown below are parallel lines n and p which are cut by transversals r and s which are perpendicular to each other. Which of the following is the measure of 21?
(1) 51
(2) 64
(3) 72
(4) 102

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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?