1. **State the problem:** Calculate the simple interest rate given principal $P=1,440,000$, interest $I=72,000$, and time $T=1\frac{1}{2}$ years. 2. **Formula for simple interest rate:** The simple interest formula is: $$I = P \times r \times T$$ where $r$ is the interest rate per year. 3. **Rearrange to find $r$:** $$r = \frac{I}{P \times T}$$ 4. **Substitute the values:** $$r = \frac{72,000}{1,440,000 \times 1.5}$$ 5. **Calculate the denominator:** $$1,440,000 \times 1.5 = 2,160,000$$ 6. **Calculate the fraction:** $$r = \frac{72,000}{2,160,000}$$ 7. **Simplify the fraction:** $$r = \frac{\cancel{72,000}}{\cancel{2,160,000}} = \frac{1}{30}$$ 8. **Convert to percentage:** $$r = \frac{1}{30} = 0.0333 = 3.33\%$$ **Final answer:** The interest rate is **3.33% per year**.