A simple rule of thumb for determining your maximum safe heart rate (in beats per minute) is to subtract your age from 220. While exercising, you should maintain a heart rate between 60% and 85% of your maximum safe rate.
(A) Find a linear model for the minimum heart rate m that a person of age x years should maintain while exercising.
(B) Find a linear model for the maximum heart rate M that a person of age x years should maintain while exercising.
(C) What range of heartbeats should you maintain while exercising if you are 20 years old?
(D) What range of heartbeats should you maintain while exercising if you are 50 years old?