Your example shows that you add a 0 to the end of how many heartbeats you get throughout 6 seconds which was 7 so that would give you 70, however in Sarah's example it doesn't tell us how many times her heartbeats in 6 seconds so I can't give you the answer, but if that's how the question is supposed to be then the answer would be 60 for all.
I hoped that helped! Let me know if you have any questions!
Have a great day/night! :)