Harry Whipple, owner of an inkjet printer, has agreed to allow Mary and Natalie, two friends who are pursuing master's degrees, to print several papers for their graduate courses. However, he has imposed two conditions. First, they must supply their own paper. Second, they must pay Harry a fair amount for the usage of the ink cartridge. Harry's printer takes two types of cartridges, a black one and a color one that contains the inks necessary to print in color. Black replacement cartridges cost $$25\mathrm{.}50$ each and print approximately $850$ pages. The color cartridge replacement cost $$31$ and prints approximately $310$ color pages. One ream of paper costs $$2\mathrm{.}50$ and contains $500$ sheets. Mary's printing requirements are for $500$ pages, while Natalie's are for $1,000$ pages.