Annual income for ages 25 to 85 is given graphically. People sometimes spend less than their income (to save for retirement) or more than their income (taking out a loan). The process of spreading out spending over a lifetime is called consumption smoothing.
(a) Find the average annual income for these years.
(b) Assuming that people spend at a constant rate equal to their average income, when are they spending less than they earn, and when are they spending more?

annual income ($1000s per year) 40 20 25 45 65 85 Age (years)