The cardiac output is the amount of blood pumped by the heart per minute. Necessarily, the cardiac output is the product of the heart rate, which is the number of beats per minute, and the stroke volume, which is amount pumped per beat. The cardiac output is usually expressed in litres/minute. So if the cardiac output is 5250ml per minute and the heart rate is 75 beats/min, the stroke volume would be 70 ml/beat.
Cardiac output = stroke volume × heart rate
5250 ml per minute = Stroke volume * 75 beats per minute
Stroke volume = 5250 /75
So the stroke volume is 70 ml