If you start with 45 million and then add 45 million every 4 years, it would take approximately 138 years to reach 1.6 billion.

Would you like any further explanation or have additional questions? Here are some related questions:

1. How would the number of years change if the starting amount was less than 45 million?
2. What would the total be after 120 years?
3. How many 4-year periods would it take to reach 2 billion?
4. What if the addition amount was 30 million every 4 years instead of 45 million?
5. How would the result change if the time interval was 5 years instead of 4?

Tip: Always double-check your units when dealing with large numbers to ensure accuracy in your calculations.