Why is the sign of the number that is multiplied by the hours negative?

An an average person has 6×10 by the power of two as many red blood cells as white blood cells a small sample of the blood has 7×10 by the power of three white blood cells about how many red blood cells are in the sample

Which graph represents the following piecewise defined function?

Eden has a part time job. she is paid ? 7.20 an hour the week she worked 18 and a half hours how much is she paid