Good Afternoon

Can I please have some assistance with the question below

Dave offered and Steve has agreed verbally to pay $15,000 for Steven's rare collection of coins. Before the matter can proceed any further Steve is involved in a serious car accident that results in him entering a coma. It is uncertain whether Steve will regain consciousness. Worried about Steve but still eager to purchase the coin collection, Dave consults you to ascertain what essential elements required to give rise to a valid contract are present in this situation. Advise Dave on this point and explain what facts may prevent the existence of a valid contract