1. **Problem statement:** We have a rhombus with angles labeled 135°, $y$, 45°, and 315°. We need to find the size of angle $y$ and observe the relationship between opposite angles in the rhombus. 2. **Recall properties of a rhombus:** All sides are equal in length, and opposite angles are equal. Also, the sum of the interior angles in any quadrilateral is $360^\circ$. 3. **Sum of angles:** Let the four angles be $135^\circ$, $y$, $45^\circ$, and $315^\circ$. Their sum must be $360^\circ$: $$135 + y + 45 + 315 = 360$$ 4. **Calculate $y$:** $$135 + 45 + 315 + y = 360$$ $$495 + y = 360$$ $$y = 360 - 495 = -135$$ 5. **Interpretation:** A negative angle is not possible for an interior angle. This suggests the given angle measures are inconsistent for a rhombus. However, since the shape is a rhombus, opposite angles must be equal. 6. **Check opposite angles:** The top-left angle is $135^\circ$, so the bottom-right angle should also be $135^\circ$ (not $315^\circ$). The top-right angle $y$ should equal the bottom-left angle $45^\circ$. 7. **Conclusion:** - $y = 45^\circ$ - Opposite angles in a rhombus are equal. **Final answers:** - $y = 45^\circ$ - Opposite angles in a rhombus are equal.