Al hires Carl, a contractor, for the renovation of Al's bathroom at the cost of $5,000. Afl.er Carl removes Al's bathtub and toilet, Carl walks away and refuses to continue without providing any explanation. Al promises to increase Carl's fee by an additional $2,000 and they draft a new contract to memorialize this increased fee. After that, Carl returns to work and finishes the job. Does Al have to pay Carl? Why or why not? Discuss the legal principles. (If you do not state the legal principle, you will not receive credit.)