S who lives in Upington, sends P, who lives in George, a letter by private courier in which she offers to sell him her (s's) motorcycle, a collectors piece, for R 100 000. She states in her letter that her offer will expire on 1 February. P, accepts S's offer by letter, which he posts on 31 January. S receives the letter on 7 February and only reads it on the next day. P tenders payment of R100 000 but S refuses to accept payment.

did a valid contract arise between S and P? Substantiate your answer.