posted by Leslie .
Ken's target heart rate is 122-139bpm. His resting heart rate is 73 bpm. What is his age?
Since this is not my area of expertise, I searched Google under the key words "optimal exercise heart rate formula" to get these possible sources:
In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search. Also see http://hanlib.sou.edu/searchtools/.