Jay, Lily and Corry each plan to hold a party for their friends. The cost of each party has two parts: the cost of renting a room, and the cost of food per person. The graph shows the cost of food per person. Show your calculations for a constant rate of change to prove:
A) Whose party has the lowest cost for renting a room?
B) Whose party has the most expensive food per person?
C) Are there parallel lines in the diagram? What does this mean?