1. **State the problem:** Kristin is gluing a paper layer of thickness $0.025$ mm onto a construction board of thickness $7 \times 10^{-2}$ mm. We need to find the total thickness in scientific notation. 2. **Write the given values in scientific notation:** - Paper thickness: $0.025 = 2.5 \times 10^{-2}$ mm - Board thickness: $7 \times 10^{-2}$ mm 3. **Add the thicknesses:** $$2.5 \times 10^{-2} + 7 \times 10^{-2} = (2.5 + 7) \times 10^{-2} = 9.5 \times 10^{-2}$$ 4. **Final answer:** The total thickness is $9.5 \times 10^{-2}$ mm in scientific notation. This means the combined thickness is $9.5$ times $10$ to the power of $-2$ millimeters.