Anthony is a 42-year-old male who recently lost 50 pounds by increasing his exercise and eating small, frequent meals. Now that he is in a weight-maintenance phase, his trainer recommends doing exercise for 90 minutes per day, most days of the week, at 60-70% of his maximum heart rate. How many heartbeats per minute is 60-70% of his max heart rate?

A. 54-63 beats per minute
B. 252-294 beats per minute
C. 107-125 beats per minute
D. 132-154 beats per minute