Find the measure of x given using the interior angle theorem

The video tutorial explains how to calculate the sum of interior angles in a quadrilateral. It begins by introducing the concept of a quadrilateral having four sides. The teacher then demonstrates the formula to calculate the sum of interior angles, which is (n-2) * 180 degrees. Using this formula, the sum of the angles is calculated to be 360 degrees. The teacher proceeds to solve an equation to find the value of X, representing one of the angles, by simplifying the equation and performing arithmetic operations. The final value of X is determined to be 45 degrees, concluding the lesson.

What do the little boxes represent in the equation involving angles?

Explain how the angles in a quadrilateral add up to 360 degrees.