1. **Problem statement:** We need to find the sound level $\beta$ in decibels for a rustle of leaves with sound intensity $I = 1 \times 10^{-11}$ W/m² using the formula: $$\beta = 10(\log I + 12)$$ 2. **Formula explanation:** The decibel scale is logarithmic, meaning it measures sound intensity on a scale based on powers of 10. Here, $\log$ is the base-10 logarithm. 3. **Substitute the given value:** $$\beta = 10(\log(1 \times 10^{-11}) + 12)$$ 4. **Calculate the logarithm:** Since $\log(1 \times 10^{-11}) = \log(1) + \log(10^{-11}) = 0 + (-11) = -11$, 5. **Simplify inside the parentheses:** $$\log(1 \times 10^{-11}) + 12 = -11 + 12 = 1$$ 6. **Calculate $\beta$:** $$\beta = 10 \times 1 = 10$$ 7. **Final answer:** The sound level of the rustle of leaves is approximately **10 decibels**. This means the rustle of leaves is very quiet, as expected for such a low intensity sound.