A parallelogram has 4 sides, 2 of them are parallel to each other along with the others. You can see how far (from the middle of the quadrilateral) is one end of the line and then indicate how far the other end is. If those numbers are equal to the other lines distance then they are parallel
The number of t-shirts a in month n is 70% of the number of t-shirts in month n-1 plus 25 because they always sell 30% of the t-shirts and get 25 t-shirts in shipments. can be included as an after-thought.
