Can somebody help me

Which statement about perfect cubes is true

Simply 8x squared + 5(7x squared- x) - 2x =

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?