I believe it is c 100x because you multiply the 10 by the power of the eye piece which is usually 10 and 10 multiplied by 10 is 100
Your heart rate before exercising would probably be the at rest rate of say about 50-60 beats per minute whereas immediately after exercise it could easily be say 115-130 and depending on age there is an optimum heart rate for each age range which decreases somewhat with age. Timing for a full minute your heart rate is best as it will give the actual count whereas if you just do it for 10 seconds and then multply by 6 it would assume it will be consistent whereas it could decrease during the minute so the actual measured count for a full minute is more accurate.
Answer:
Cells divide so living things can grow. When organisms grow, it isn't because cells are getting larger. Organisms grow because cells are dividing to produce more and more cells.