1. **State the problem:** Simplify the expression $$-\frac{3i}{72}$$ and write the answer in the form $a + bi$. 2. **Simplify the fraction:** The fraction $$-\frac{3i}{72}$$ can be simplified by dividing numerator and denominator by their greatest common divisor, which is 3. 3. **Show intermediate step with cancellation:** $$-\frac{\cancel{3}i}{\cancel{72}} = -\frac{i}{24}$$ 4. **Rewrite in standard form:** The expression is now $$0 - \frac{1}{24}i$$, which is in the form $a + bi$ with $a=0$ and $b=-\frac{1}{24}$. 5. **Final answer:** $$0 - \frac{1}{24}i$$ or simply $$-\frac{1}{24}i$$.