Mark and Jessica are middle-aged homeowners, who live in a 5,500 square foot mansion in New Jersey that has radiant electric floor heat with separate zones throughout the house. This past winter, their kitchen zone was not working. Instead of tearing apart their entire kitchen to find the fault in the floor, they decided to start getting estimates from licensed plumbers to put in hydronic radiant floor heat. This type of heat can be put in under their current system and it uses hot water to heat the floors. They first called Working Pipes Plumbing for an estimate, which came back at $32,000. They then called Hall Andrews Plumbing and their estimate was $22,000. Mark and Jessica responded to both Working Pipes and Hall Andrews’ estimates by stating that they only wanted to spend $20,000. Working Pipes then walked away but Hall Andrews promised to perform the services and Mark and Jessica promised to pay them $20,000. Mark and Jessica and Hall Andrews then put everything in writing and they both signed the document.
Suppose Hall Andrews had told Mark and Jessica that he would do the work. Mark and Jessica then agreed that he could do the work but did not agree to give him anything in return. In this situation, which element of a valid contract would be missing?