Which scenario represents a unilateral contract?

A unilateral contract exists when one party makes a promise in exchange for an act by another party, without the other party making a reciprocal promise. In the scenario where Sherry offers to give Brent a ride home, Sherry is the only one making a promise—she has committed to providing the ride. Brent does not need to make any promises or commitments concerning the ride; his acceptance occurs through his action of accepting the ride. The contract is established solely by Sherry's offer and Brent's eventual acceptance through his behavior, which is the hallmark of a unilateral contract.

In contrast, the other scenarios represent different contract types. When Brent agrees to share expenses for the trip, that's a mutual agreement, signifying a bilateral contract where both parties have made promises. Similarly, when Sherry and Brent mutually agree to the terms of the ride, it also creates a bilateral contract because both are making promises to each other. Lastly, if Brent promises to pay Sherry for the ride, that establishes another bilateral agreement since both parties are promising to perform. This distinction clarifies why the first scenario is accurately identified as a unilateral contract.