Final answer:
The estimated number of heartbeats in a lifetime is approximately 2,837,040,000 beats, which is closest to 5 billion (d).
Step-by-step explanation:
The answer is d) Approximately 5 billion. The estimated number of heartbeats in a lifetime can be calculated by multiplying the average heart rate in beats per minute by the number of minutes in a lifetime. Assuming an average heart rate of 72 beats per minute, and an average lifespan of 75 years, which is approximately 39,420,000 minutes, the approximate number of heartbeats in a lifetime would be:
72 beats/minute x 39,420,000 minutes = 2,837,040,000 beats
Therefore, the closest option is approximately 5 billion (d).