To find the measure of the unknown angle in a quadrilateral, we need to use the property that the sum of all interior angles in any quadrilateral is 360°.

From the image, the angles provided are:

1. 43°
2. 140°
3. 40°

Let the unknown angle be represented as $x$.

According to the sum of angles in a quadrilateral: $43^\circ + 140^\circ + 40^\circ + x = 360^\circ$

Combining the known angles: $223^\circ + x = 360^\circ$

Now, subtract 223° from both sides to find $x$: $x = 360^\circ - 223^\circ = 137^\circ$

The measure of the unknown angle is 137°.

Would you like a detailed explanation of the steps, or do you have any questions?

Here are five related questions to consider:

1. What is the sum of interior angles for different polygons?
2. How can you find an unknown angle in a triangle?
3. Why do the interior angles in a quadrilateral add up to 360°?
4. How would the solution change if this were a pentagon?
5. What is the difference between interior and exterior angles in polygons?

Tip: In any polygon, the sum of interior angles is $(n - 2) \times 180^\circ$, where $n$ is the number of sides.