Answer: 75 beats per minute
Step-by-step explanation:
To calculate heart rate from cardiac circle, all you need do is to calculate the time taken for one cardiac circle (in this case, it is 0.800secs). Then divide sixty seconds (1min) by 0.8 and whatever you get as an answer will be your heart rate in beats per minute.
So the answer to the question will be:
60/0.8 =75bpm