profitable investment

Which is the most profitable investment for a cell phone company earning $10 per plan contract?
opening a new store location with $200 daily operating cost, generating 30 new plans per day
redesigning web site at $50 daily operating cost, generating 10 new plans per day
creating television commercial at $25 daily operating cost, generating 15 new plans per day
offering free $10 gift for every new plan, generating 40 new plans per day