The graph shows the motion of two cars starting at different places on a highway. Their speeds can be compared by comparing the steepness of the graphed lines. Use the drop-down menus to complete the statements.

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?