ANSWER:
While doing the aerobic exercise, heart rate must be in the range of 144.2 bpm to 175.1 bpm for a 14 years old person.
SOLUTION:
Given, your heart rate rises when you exercise.
During aerobic exercise, your heart rate should be at least 0.7(220 - a), but no more than 0.85(220 - a), where “a” is your age.
We need to find the target range if you are 14 years old.
Here a = 14
For 14 years old, lower range is
0.7(220 – 14)
0.7(206)
144.2
Now, for 14 years old, upper range is
0.85(220 – 14)
0.85(206)
175.1
Hence, while doing the aerobic exercise, heart rate must be in the range of 144.2 bpm to 175.1 bpm for a 14 years old person.