To solve this problem, we can set up a mathematical equation.

You start with 45 million and add 45 million every 4 years. The total amount $T$ after $n$ periods of 4 years can be expressed as:

$T = 45 \text{ million} + 45 \text{ million} \times n$

where $n$ is the number of 4-year periods.

We want to find out when $T$ reaches 1.6 billion:

$45 \text{ million} + 45 \text{ million} \times n = 1.6 \text{ billion}$

First, let's convert everything to millions for simplicity:

$45 + 45n = 1600$

Next, subtract 45 from both sides:

$45n = 1600 - 45$ $45n = 1555$

Now, divide by 45:

$n = \frac{1555}{45} \approx 34.56$

So, it would take about 34.56 periods of 4 years each to reach 1.6 billion.

Finally, multiply by 4 to convert the number of periods into years:

$\text{Years} = 34.56 \times 4 \approx 138.24$

Thus, it would take approximately 138 years to reach 1.6 billion.

Would you like further details on this solution or have any additional questions? Here are some related questions:

1. How would the time change if the initial amount was different?
2. What would be the total after 50 years?
3. How many years would it take to reach 1 billion instead of 1.6 billion?
4. What if the addition amount was increased to 60 million every 4 years?
5. How does the result change if the addition is every 3 years instead of 4?

Tip: When solving similar problems, it's helpful to convert all numbers to the same unit to simplify calculations.