1. **Problem:** Find the value of $\angle BCA$ in the triangle where the side opposite $B$ is labeled $2x$. 2. **Formula and rules:** In any triangle, the sum of interior angles is always $180^\circ$. 3. **Step 1:** Identify the angles in the triangle. Let the angles be $\angle BAC$, $\angle ABC$, and $\angle BCA$. 4. **Step 2:** Since the side opposite $B$ is $2x$, assume $\angle ABC = 2x$ (if the problem implies this). 5. **Step 3:** If no other angles are given, we need more information to solve for $\angle BCA$. Since the problem only gives $2x$ opposite $B$, and no other data, we cannot find a numeric value for $\angle BCA$ without additional information. **Conclusion:** The problem as stated does not provide enough information to find $\angle BCA$. Please provide more details or angle measures.