Question is related to Contract Law in the U.K

Rohan is a keen cyclist who runs his own business repairing bicycles. He rents a small lock-up workshop from Hansaj. Six months ago he met with Hansaj. and explained that he had been suffering financial difficulties and might have to close his business. Hansaj, realising that he would have difficulty finding another tenant for the workshop agreed to reduce the rent by 50 per month.

Two months ago, Rohan managed to negotiate a lucrative contract to service and repair the bicycles of the Chester cycling club.

Yesterday Rohan met Sheila at his friend Krishna's house. Sheila, Krishna's cousin, had cycled round to the house. On the way there, however, there was a problem with the cycle's brakes and she had been unable to change gear properly. Sheila was worried about riding the cycle in its current condition and so asked Rohan to have a look at it for her. He repaired the cycle relatively quickly, but Sheila was so grateful she said she would send him 30. Rohan was surprised. He said that he had been happy to help out but thanked her, saying the money would come in useful.

Hansaj has just found out about Rohan's lucrative contract and is now demanding he resume paying the original rent. He is also demanding the sum of 100 being the difference between the original rent and reduced rent for the past two months.

Rohan has not received 30 from Sheila.

Advise Rohan:

• whether he will have to resume paying the original rent, and is liable to pay the sum of 100 to Hansaj; and
• whether he is entitled to 30 from Sheila.

you must:

• Define consideration.
• Explain the common law position in relation to part payment of a debt.
• Explain the doctrine of promissory estoppel.
• Explain if, and when, a past act may be consideration.
• Apply the law to the facts and cite relevant authorities.