1. **State the problem:** We have two parallel horizontal lines $m$ and $n$ intersected by a transversal line $p$. An angle of $43^\circ$ is formed at the intersection of $p$ and $m$ on the top left side, and we need to find the value of angle $x^\circ$ at the intersection of $p$ and $n$ on the bottom right side. 2. **Relevant rule:** When two parallel lines are cut by a transversal, alternate interior angles are equal. 3. **Identify alternate interior angles:** The angle $43^\circ$ on line $m$ and the angle $x^\circ$ on line $n$ are alternate interior angles. 4. **Apply the rule:** Since $m \parallel n$, we have $$x = 43^\circ$$ 5. **Conclusion:** The value of $x$ is $43$ degrees.