1. **State the problem:** We need to find the value of angle $x$ in a figure where there is a triangle adjacent to a straight line segment with an angle of 120 degrees at point $R$. 2. **Recall the rule:** The angles on a straight line add up to 180 degrees. 3. **Apply the rule:** Since the angle at $R$ is 120 degrees, the adjacent angle on the straight line, which is $x$, satisfies: $$x + 120 = 180$$ 4. **Solve for $x$:** $$x = 180 - 120$$ $$x = 60$$ 5. **Conclusion:** The value of angle $x$ is 60 degrees.