A valid contract was formed because there was an offer, acceptance, and consideration—the agreement to purchase the property for $150,000 and the $15,000 down payment. There are no facts suggesting any defenses to formation such as fraud, duress, or mistake, so the contract is enforceable. The provision stating that Smith may retain the $15,000 if Brown breaches is an express term, meaning it is explicitly written into the contract. Courts generally enforce clear and unambiguous express terms unless they violate public policy. Brown failed to perform his obligation to purchase the condominium, which constitutes a material breach because he refused to complete the transaction before closing. Although this breach appears willful, that does not automatically bar restitution, so answers A and B are incorrect since modern law allows breaching parties to seek restitution in some circumstances. The clause allowing Smith to retain the $15,000 is a liquidated damages clause, which is a provision that sets damages in advance in the event of a breach. Such clauses are enforceable so long as they are a reasonable estimate of anticipated damages and not a penalty. There is no issue here involving a condition, as this case concerns breach and the enforcement of a damages provision rather than the failure of a condition precedent. A liquidated damages clause will not be enforced if it is unreasonably large and operates as a penalty. However, there is no indication that $15,000 is excessive in relation to a $150,000 contract. Because the amount appears reasonable on its face and the facts do not suggest otherwise, the clause is presumed valid. Therefore, because the contract expressly provides that the down payment will be retained as liquidated damages upon breach, and the clause is enforceable, Brown is not entitled to recover the $15,000.