We are given that the sum of the interior angles of the given quadrilateral is 360^(∘). Knowing this, we can write an equation that adds all of the angles together and is equal to 360^(∘).
x+100+120+100=360
Solving this equation for x will give us the measure of the unknown angle.
We will now use a protractor to check if our answer is reasonable. We begin by placing the center of our protractor on the corresponding vertex while the straight part of the protractor is on one side of the quadrilateral.
Next, we need to determine whether the inner or outer measuring scale should be used. Since the measuring scale that has 0 on the side of the quadrilateral is the outer number, we will use the outer scale.
We can see that the sides that form angle x pass through 0 and 40 in our protractor. Therefore, the measure of the angle is 40^(∘), which is the same result we got from solving the equation.
