Pawtucket University is planning to buy new copier machines for its library. Three members of its Management Science Department are analyzing what to buy. They are considering two different models: Model A, a high-speed copier, and Model B, a lower speed but less expensive copier. Model A can handle 20,000 copies a day and costs $6,000. Model B can handle 10,000 copies a day but only costs $4,000. They would like to have at least six copiers so that they can spread them throughout the library. They also would like to have at least one high-speed copier. Finally, the copiers need to be able to handle a capacity of at least 75,000 copies per day. The objective is to determine the mix of these two copiers that will handle all these requirements at minimum cost. 

a. Formulate and solve a spreadsheet model for this problem. 

b. Formulate this same model in algebraic form.