Answer:
The correct option is;
a) Mike, he is within his target heart rate zone
Step-by-step explanation:
The Target Heart Rate Zone (THRZ) is the range of the percentage of a person's maximal heart beat rate (MHR) targeted to be achieved during exercising. It is a very good way to gauge the comparative intensity of a person's exercise
Whereby, Joe's heart beat rate is below his THRZ and Mikes heart beat rate is within his THRZ, Mike is working harder.
Hence the correct option is (a) Mike, he is within his target heart rate zone.