Someone please help me solve this: - 2x + 10 + 5x = 40​

Pls me this is due today and i need i will make brainliest if you me answer correctly and i will report if you try to give me a dumb answer.

Find the number of liters in 12.8 gal of gasoline. round to the nearest hundredths

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?