Use your knowledge of the law of contract to provide suitable advice for the following scenario in 400–600 words. David enters into a contract to supply Adam with Italian marble tiles. The contract stipulates that 1,000 tiles are to be delivered monthly, for 24 months, at a fixed price payable in equal monthly installments. Four months later the market price of marble tiles unexpectedly doubles and David tells Adam he cannot supply the tiles at the contract price, it is liable to bankrupt him, and he will have to cancel the contract. Adam suggests to David that he would be prepared to take 750 tiles per month for the agreed contract price, and David is relieved and agrees. Delivery continues on this basis for the next six months, during which time the market price of marble gradually decreases until it is back to the price it was at the date of the original contract. Adam now tells David he wants the shortfall in delivery for the past six months made good next month and a return to the original quantity of 1,000 tiles delivered each month for the next 14 months left under the contract. Advise David: a. whether the variation agreement to the original contract is binding; and (10 marks) b. to what extent the variation might be enforceable under the doctrine of promissory estoppel.