Wise Company, a property investment company, purchased flats with a view of letting them for receiving rental revenue. On March 15, 2020, the company purchased twelve residential flats of a building and signed a lease with Nice Company for two years for letting the twelve residential flats to Nice Company as staff dormitory after refurbishment of the flats. It was agreed that vacant possession of the flats will be delivered to Nice Company on April 15, 2020. Wise Company would have to pay Nice Company $10,000 per day if vacant possession of the flats could not be delivered in time.

On March 16, 2020, Wise Company engaged three contractors, Alex, Boris and Charles, to carry out the renovation of the flats. Each of them would finish the renovation work of four flats by April 14, 2020. The contract price of $100,000 would be paid to each of them upon completion of their work.

At the end of March, Alex told Wise Company that he would not complete his work in time unless Wise Company agreed to increase a further payment of $10,000. Since no replacement could be found within such a short period, Wise Company agreed to pay the increased sum in order to ensure that the work would be completed on time.

At the same time, since Wise Company prepared to demonstrate in advance of the renovation work to its top management, Boris was asked if he could complete his work by April 10, 2020 by increasing an additional $10,000 to the original contract price. Boris agreed to finish his work by April 10, 2020.

In consideration of fairness, Wise Company also promised Charles a bonus of $10,000 if the job was done on time as agreed.

Eventually, Alex completed his work on April 14, 2020. Boris completed his work on April 10, 2020 as requested by Wise Company. Charles also completed his work on April 10, 2020, four days earlier than the agreed completion date. However, Wise Company has now refused to make any additional payments of $10,000 beyond the original contract price to Alex, Boris and Charles.

Does the company needs to keep the promise to pay the extra $10,000 to Alex, Boris and Charles?