Jonnel Enterprises, Inc., contracted to construct a student dormitory at Clarion State College. On May 6, Jonnel entered into a written agreement with Graham and Long as electrical contractors to perform the electrical work and to supply materials for the dormitory. The contract price was $70,544.66. Graham and Long claim that they believed the May 6 agreement obligated them to perform the electrical work on only one wing of the building, but that three or four days after work was started, a second wing of the building was found to be in need of wiring. At that time Graham and Long informed Jonnel that they would not wire both wings of the building under the present contract, so a new contract was orally agreed upon by the parties. Under the new contract Graham and Long were obligated to wire both wings and were to be paid only $65,000, but they were relieved of the obligations to supply entrances and a heating system. Graham and Long resumed their work, and Jonnel made seven of the eight progress payments called for. When Jonnel did not pay the final payment, Graham and Long brought this action. Jonnel claims that the May 6 contract is controlling. Is Jonnel correct in its assertion? Why?