Using a unit level analysis how do I develop a graph with who lines showing cost structures in two different time periods?

The question does not give specific information just "Homestead Telephone was formed in the 1940s to bring telephone services to remote areas of the US Midwest. The early equipment was quite primitive by today's standards. All calls were handled manually by operators, and all customers were on party lines. By the 1970's, however, all customers were on private lines, ad mechanical switching devices handled routine local and long distance calls. Operators remained available for directory assistance, credit card calls and emergencies. In the 1990s Homestead Telephone added local internet connections as an optional service to its regular customers. It also established an optional cellular service, identified as Home Ranger.