I do not understand the difference between a and b. Can you please help me to understand?

Scatter Diagrams and High-Low Cost Estimation Assume the local Pearle Vision has the following information on the number of sales orders received and order-processing costs. Month Sales Orders Order-processing Costs 1 ,500 4400 2,300 1 ,200 Required 82,700 50,375 120,700 81 ,goo 69,775 43,100 62,500 (a.) Use information from the high- and low-volume months to develop a cost-estimating equation for monthly order-processing costs. 14000 24.25 (b.) Plot the data on a scatter diagram. Using the information from representative high-and low-volume months, develop a cost estimating equation for monthly production costs. If needed, an Excel worksheet is provided in the following link in order to create the scatter diagram: Scatter_Diagram xL+S