1. **State the problem:** Simplify the expression $6m^{-2} n^{-1} + 3m^{-2} n^{-1}$. 2. **Recall the rules:** When adding terms with the same variables and exponents, you can add their coefficients directly. 3. **Identify like terms:** Both terms have $m^{-2} n^{-1}$, so they are like terms. 4. **Add the coefficients:** $$6 + 3 = 9$$ 5. **Write the simplified expression:** $$9m^{-2} n^{-1}$$ 6. **Rewrite with positive exponents:** $$9 \times \frac{1}{m^{2}} \times \frac{1}{n} = \frac{9}{m^{2} n}$$ **Final answer:** $$\frac{9}{m^{2} n}$$