did i work these problems right if not could some one show me how to work all three of them.

Question

8.Represent the quantity with a real number: An altitude of 400 feet (ft) above sea level: 400 is a real number. I could also use 4 as a real number representing a 400 ft. altitude as 4 increments of 100 feet as in flight level 4

9.Represent the quantity with a real number: A loss of $200 = -200

10.Represent the quantity with a real number: A decrease in population of 25,000 = -25,000