3 + (5 + 4) = 3+ (4 + 5) illustrates which property?

The polygon tool to draw a rectangle with a length of 5 units and a height of 3 units. one of the sides of the rectangle falls on line ab , and the rectangle has a vertex of a. each segment on the grid represents 1 unit.

What is the measure of angle x? 37° 82° x°

Zahra wants the equation below to have an infinite number of solutions when the missing number is placed in the box.