You must know rour resting heart rate before you can calculate your target heart rate for exercise. Correct answer: B Resting heart rate is the number of times the heart beats per minute when te body is at rest. It is usually somewhere between 60 and 100 beats per minute for the average adult. In order to calculate the target heat rate, you should calculate heart rate reserve (HRR) which is resting heart rate subtracted from your maximum heart rate. Then you should m ultiply your HRR by 0.7 (70 percent) and add your resting heart rate to this number and ultiply your HRR by 0.85 (85 percent) and add your resting heart rate to this number. This is the taregt zone.