Answer is B
How I got is because I had to first figure out what 40 seconds worth of heartbeats are equal to. 80 - 48 is 32 divided by 2 is 16. Next, I added 48 and 16 which got me 64. All I had to do next was to add 80 and 16 because the rate of heartbeats per 10 seconds is 16. 80+16=96 and thats how I figured that the answer is B