One size of cardboard can be purchased in sheets that are 3 16 inch thick. The sheets of cardboard are stacked on top of each other in packages. The height of each stack is 2 1 4 inches. A segment of a ruler showing just over four inches. Use the model of a ruler to determine the number of sheets of cardboard in a stack. Explain how you used the model to find your answer. Write an expression that can be used to determine the number of sheets of cardboard in a stack. Explain how your expression relates to the model.