In this question, you are asked the time but given the speed(89beat/min) and the number of beats(3.1 x 10^9). Then the equation would be:
Time= number of beats/ speed
Time = 3.1 x 10^9 beats / (89 beats/min)= 3.483 x 10^7 minutes.
Then convert it to years, disregard of leap years it would be : 3.483 x 10^7 minutes / (60 minutes/hour) / (24 hour/day) / (365 day/year)= 66.26 years
