1. The problem is to find the missing base growth factor in the compound interest expression: $$20000 \times \Box^3$$ where the interest rate is 4% per year and the time is 3 years. 2. The formula for compound interest growth factor per year is: $$1 + \frac{r}{100}$$ where $r$ is the interest rate percentage. 3. Since the interest rate $r = 4$, the growth factor per year is: $$1 + \frac{4}{100} = 1 + 0.04 = 1.04$$ 4. Therefore, the missing number in the box is $1.04$. 5. The full expression becomes: $$20000 \times 1.04^3$$ which calculates the amount after 3 years with 4% compound interest. Final answer: The missing number is $1.04$.