Jeremy has a dispute with a local tree removal company. After a big storm had come through the area, Jeremy had to hire the company to remove a big tree. The two parties had agreed to the price of $1,500. However, the company never finished the job. The company left when the tree was only half removed. Jeremy and his dad finished the rest of the removal two weeks later. Jeremy does not think he owes the tree removal company anything. The tree removal company however wants to be paid. Jeremy offers them $500 in settlement of their dispute. The tree company accepts. This agreement can best be described under contract law as ______________________.