Answer
My heart will beat $3.786912 \times 10^{9}$ times during my lifetime.
Work Step by Step
There are 60 minutes in one hour so the heart beats $80(60)=4800$ times in on hour.
There are 24 hours in a day so the heart beats $4800(24) = 115200$ times in a day.
There are $365\frac{1}{4}$ days in a year so the heart beats $115,200(365.25) = 42,076,800$ in a year.
Thus, if I live for 90 years, my heart will beat a total of
$42,076,800(90) = 3,786,912,000$ times.
Writing this in scientific notation gives:
$3,786,912,000 = 3.786912 \times 10^{9}$
