1. **State the problem:** Express the given number as a power of 3. 2. **Formula and rules:** A number expressed as a power of 3 is written as $3^n$ where $n$ is an integer. 3. **Example:** Suppose the number is 27. 4. **Intermediate work:** Since $27 = 3 \times 3 \times 3 = 3^3$, we write $27 = 3^3$. 5. **Explanation:** We find the exponent $n$ such that $3^n$ equals the given number by repeated multiplication or by using logarithms. 6. **Final answer:** The number expressed as a power of 3 is $3^3$ if the number is 27. If you provide a specific number, I can express it as a power of 3.