On June 1, Butt Construction Ltd. ("Butt") entered a contract with Tom and Audrey Smith to construct a custom home on their land.Under the contract terms, Butt agreed to complete the home by September 30 or incur a 10% financial penalty for not completing the construction by that date. In turn, Butt entered into a contract with Quality Framing Ltd. ("Quality Framing") to do the wall and roof framing for the house.The terms of this subcontract between Butt and Quality Framing required Butt to pay $50,000 on completion of the framing work, which was scheduled to be completed by July 20.

Quality began work immediately, but unfortunately June was an unusually rainy month, which put Quality behind in its framing work.In order to complete on time, Quality was going to have to pay its workers overtime and this would wipe out all its profit for the job.Accordingly, Quality went to Butt on June 28 and indicated that to meet the July 20^thframing deadline it would require an additional $15,000 under the subcontract to pay for the required overtime in labour.

Butt did not like the idea of paying an extra $15,000, but the time it would take to find another framer was too long and it needed the framing done by July 20 to meet its own deadline of September 30 and avoid a significant financial penalty.Consequently, Butt's president signed a document agreeing to pay Quality an additional $15,000.

On July 20 Quality Framing finished the framing work and submitted its invoice for $65,000 (the original $50,000 and the additional $15,000 premium).On July 30, Butt delivered a cheque to Quality Framing in an envelope.When the president of Quality Framing later opened the envelope, he saw that the cheque was for only $50,000, the original price.

3. Is the written agreement wherein Butt agreed to pay Quality Framing an additional $15,000.00 legally enforceable?If so, why?If not, why not?Please support your answer with reference to the law and the facts.