Use the normal ecg trace below to determine how many seconds the trace represents as well as the heart rate.

Attached is the image of the concerned ECG reading.

In reading the ECG, first you read the heart rate. To read the heart rate, you must count for the number of small boxes in between QRS complexes, specifically R-R intervals. These number of small boxes will then be used to divide 1500. In this example, there are 20 small boxes between R-R intervals. 1500 divided by 20 is 75, so the heart rate of this ECG reading is 75 beats per minute. 

Another way, albeit less accurate, is to count the big squares between R-R intervals and instead of dividing it by 1500, you divide it by 300.

What are the options?