ELI5: Explain Like I'm 5

Rectangle method

Rectangle Method is a way of estimating the area underneath a graph. It works by taking the area of the rectangle and adding them up. To do this, you split the graph into a bunch of smaller rectangles. Then you count how many rectangles there are and then find the area of each rectangle. Finally, you add up all of the rectangles' areas to get the total area under the graph.