Lucas purchased 4 large posters and 6 small posters online and spent $21 on shipping. he spent x to ship each small poster and twice as much to ship each large poster. what is the cost of shipping a small poster? explain your thinking.

Which statement explains how you could use coordinate geometry to prove the opposite sides of a quadrilateral are congruent? a. use the slope formula to prove the slopes of the opposite sides are the same. b. use the slope formula to prove the slopes of the opposite sides are opposite reciprocals. c. use the distance formula to prove the lengths of the opposite sides are the same. d. use the distance formula to prove the midpoints of the opposite sides are the same.