Answer:
the point is that SB is the same length and BU... see? even thou, the box is a parallelogram... so 1/2SU= BU or 21 :) maybe by intution it seems like one side might be longer than the other but. b/c both sides have to move.. the line stays the same on each side.. so the crossing point. is half way... always.. :o
Step-by-step explanation:
