SingSong Supermarket had 10 employees; serving as cashiers and replenishing staff. During the recent outbreak of the coronavirus in Singapore, five of the cashiers and replenishing staff, who lived in the same dormitory, were confined for two weeks having come into contact with a person who was tested positive for the virus.

Upon hearing that five of his staff had to be confined for two weeks, and in an effort to avoid disruption of business operations, the owner of SingSong Supermarket, Nelson Goh, told the remaining staff that if they took over the roles of the staff who were confined, on top of their own duties, he would double their wages for two weeks until the confined staff returned to work. The staff agreed and put in the extra effort to keep the business running.

Two weeks had passed, and the confined staff have returned. Nelson now refuses to pay the extra wages promised to the staff who were not confined, considering that it was their job to keep the supermarket going.

Using your understanding of consideration under contract law, suggest if Nelson is obliged to keep his promise of extra payment to the staff in question.

(10 marks)