This Problem Set is a part of the Lesson 19, Unit 6, Grade 7. Practice Problems: Lin missed math class on the day they worked on expanding and factoring. Kiran is helping Lin catch up. Lin understands that expanding is using the distributive property, but she doesn't understand what factoring is or why it works. How can Kiran explain factoring to Lin? Lin asks Kiran how the diagrams with boxes help with factoring. What should Kiran tell Lin about the boxes?