1. **State the problem:** We need to find angle $A$ in a triangle given side $b$. 2. **Identify what is missing:** To find an angle in a triangle, we need more information than just one side. Typically, we need either two sides and an included angle (SAS), two angles and a side (AAS or ASA), or all three sides (SSS). 3. **Formula used:** If we had all three sides $a$, $b$, and $c$, we could use the Law of Cosines: $$\cos A = \frac{b^2 + c^2 - a^2}{2bc}$$ 4. **Explanation:** The Law of Cosines relates the lengths of the sides of a triangle to the cosine of one of its angles. Without knowing at least two sides or an angle, we cannot determine angle $A$. 5. **Conclusion:** Since only side $b$ is given, it is impossible to find angle $A$ without additional information such as other sides or angles.