contract law - binding contract?

In general, an advertisment is not an offer but only an invitation to treat (Partidge v Crittenden) or a declaration of intention. Hence, T was not making an offer to sell the camera but inviting others to make an offer to buy the camera. It follows that S and K were both making offers to T.
No information shows that S's offer was accepted by T. For K, his offer was not yet communicated to T on 5/10. T could not have accepted K's offer without knowing it existence. Thus no contract was formed between the parties yet.
An exception to the above is unilateral contract where an advertisement specifying the way of acceptance by performance of some act may be an offer (Carlill v Carbolic Smoke Ball Company).
T specified a deadline in his advertisement. Does this make Carlill case applicable could be arguable but it is more likely that it resembles the situation of setting a deadline for submiting tender. Inviting tender is only invitation to treat (Blackpool Aero Club v Blackpool Borough Council) and tendereres are making offers. It remains that S and K were making offers yet to be accepted by T.
But if it can be established that Carlill is applicable and T was making an offer:
- By application of the postal rule, S's acceptance took place on 4/10, i.e. before T's revoke his offer on 6/10. Hence, a binding contract was formed between S and T.
- For K, his phone call on 5/10 did not amount to acceptance as acceptance will not be valid until it is actually communicated to T, the offeror (Entores v Miles Far East Corp.). T revoked his offer on 6/10 and thus K could not later accept it during his visit to T's house on 7/10. Thus no contract was formed between T & K.

the contract is binding between S and T however not between K and T

since before T decides to end the contract , K did not make it clear to T of his intention to buy the camera

however according to the postal rule , the day the contract binds is the day that S posted the letter with the cheque...