Hello, my name is Elton and I am working on my homework for AP Calculus. I am using Houghton Mifflin's Calculus of a single variable: eighth edition. Currently, I am on section 4.2 which is mainly based on area. If anyone understands it completely, can you please put it in laymen's terms? I really don't understand it and this work was due on Friday, but I got an extended due date.

PS: Everything seems to be in a whole another language to me.