1. **State the problem:** Calculate the value of the expression $\left(-\frac{5}{6}\right) \times 12 + 3.5$. 2. **Apply multiplication first:** Multiply $-\frac{5}{6}$ by 12. $$-\frac{5}{6} \times 12 = -\frac{5 \times 12}{6}$$ 3. **Simplify the fraction:** $$-\frac{5 \times \cancel{12}}{\cancel{6} \times 2} = -\frac{5 \times 2}{1} = -10$$ 4. **Add 3.5 to the result:** $$-10 + 3.5 = -6.5$$ 5. **Final answer:** The value of the expression is $-6.5$.