Linear Programming problem dealing with airline tickets?

Question

An airline company offers flights from Phoenix to Houston and Phoenix to Salt Lake City. Each flight from Phoenix to Houston costs the airline an average of 100,000 round trip for fuel and expenses. Flights from Phoenix to Salt Lake city cost on average 56,000 round trip for expenses. An average of 400 passengers ride either flight. Passengers pay $261 for round trip ticket from Phoenix to Houston and $185 round trip from Phoenix to Salt Lake City. The airline cannot provide more than 120 round trip flights per month (for both destinations combined). Also, the number of flights to Houston should be no less than half the number of flights to Salt Lake City. How many flights to each destination should the airline offer to maximize profit?

I need help identifying my objective function and setting up the constraints, once I have that I can graph and solve but I have a hard time understanding word problems, maybe the wording is kind of confusing as well.