Woods & Steels Pte. Ltd. ("WSPL") is a construction company that specialises in refurbishing old warehouses and transforming them into hip food and beverage ("F&B") outlets. WSPL prides itself on its environmentally friendly practices by ensuring that its suppliers obtain materials from sustainable sources.

On 1st January, WSPL was engaged by Adam, the owner of an old warehouse in Pasir Panjang, to refurbish the warehouse and develop it into a F&B hub by 10th December.

WSPL wanted to find a sub-contractor to perform the carpentry work for this project. WSPL is aware that Planks Pte. Ltd. ("PPL") obtains its raw materials from sustainable sources. Therefore, WSPL offered to engage PPL for the carpentry work. WSPL prepared a contract and PPL signed it on 1st February. Under the terms of the written contract, PPL is required to perform all the carpentry work for a payment sum of $250,000, and the carpentry work must be completed by 30th June.

PPL started on the carpentry work soon after the contract signing. However, PPL had difficulty in obtaining its usual supplies of American oak wood, due to a shortage in America. The alternative was to obtain European oak wood from another supplier in Europe. However, this would be more expensive for PPL, and PPL was not inclined to do so.

PPL informed WSPL that PPL would not be able to complete the carpentry work in time because of the delay in the shipment of oak wood from America. WSPL was anxious for PPL to complete its job on time, as WSPL would be subject to additional liabilities under the contract with Adam if WSPL was late in delivering the project.

The managing director of WSPL orally agreed with the managing director of PPL to increase the contract price by 10% (i.e. WSPL will pay PPL an additional $25,000), if PPL would complete the carpentry work by the original deadline, i.e. 30th June. With this promise of additional payment, PPL proceeded to order European oak wood from the European supplier and managed to complete the carpentry work by 30th June.

WSPL now refuses to pay the additional sum of $25,000 to PPL as it claims that the oral agreement was not in writing and was thus not binding.

QUESTION: Explain whether there is a valid contract between WSPL and PPL, and whether WSPL is legally obliged to pay the additional sum of $25,000. In your answer, you should identify the four (4) key elements of a valid contract, and discuss whether they were present.

NOTE: For the 4 elements of the contract, i have completed the offer and intention to create legal relations on my own. The part i need help with is the consideration and acceptance, with reference to case law. Thank you!