John needs a chiropractor. He stops in to see Dr. Stoker. John lets the good doctor know he is short on cash, and without insurance. Dr. Stoker decides to provide John with therapy for this one-time session for $500. John agrees to that price and to pay Dr. Stoker the money "when he is able." Discuss the following:

1. Who is the offeror, and who is the offeree?
2. Describe if this a bilateral or unilateral contract?
3. Does this constitute a valid, enforceable contract? Why or why not?
4. Discuss the elements of a valid contract.