Barbie owns a building in downtown Wilkes-Barre that houses a retail store selling clothing. Ken comes in one day and says "I love this building- I will offer you $500,000 for the building", also giving her a written offer. Barbie responds "I accept, but you must agree to continue operating the store in this building" and writes that on the sheet that Ken gave her. Ken leaves without saying anything. After a few days, Barbie contacts Ken with the documents of sale for the building, but Ken refuses to continue. Barbie insists they had a deal, but Ken disagrees. Who is correct and why?