A family is currently paying $40 a month for basic phone service for two phone lines. A representative from another phone carrier calls the family to offer a service that will include basic phone through a cable connection that includes two phone numbers, call waiting, voice mail, and caller-ID for $52 a month.

What additional information do they need to make the decision?

That's the one question I don't understand (from a student problem set). Can you please help me out here?