The question is asking about the associative property of addition. This involves the rearranging of the parenthesis. If you were to solve the given equation, and solve the the answer, then you will get the same answer. In this property, it says that you will get the same result if you were to move/switch the parenthesis from the values; This means that order doesn't matter.
The diameter is the line that goes through the middle of a circle and the radius goes from the center to a point in the circle so r = d/2 or d =2r C. d/2
