To achieve a moderate intensity workout according to CDC standards, Huda will most likely know she has achieved this goal when she reaches 77 percent of her maximum heart rate. Moderate intensity exercise is generally defined as 50-70% of maximum heart rate for most individuals, but 77% is often considered on the upper end of moderate or the beginning of vigorous intensity. Thus, the best option is:
when she reaches 77 percent of her maximum heart rate.