On Monday, Neil tells Outdoor Landscaping, Inc., that he will pay Outdoor $500 if a variety of tasks are completed by Friday. On Wednesday, when Outdoor is more than half done with the work, Neil says that he has changed his mind. These parties had:
a. an expired contract when Neil said that he had changed his mind.
b. a bilateral contract when Neil said that he would pay for certain work.
c. a unilateral contract as soon as Outdoor began to perform.
d. no contract.

On Monday, Neil tells Outdoor Landscaping, Inc., that he will pay Outdoor $500 if a variety of tasks are completed by Friday. On Wednesday, when Outdoor is more than half done with the work, Neil says that he has changed his mind. These parties had c. a unilateral contract as soon as Outdoor began to perform.

Explanation :

A unilateral contract is a contract created by an offer that can only be accepted by performance. To form the contract, the party making the offer  makes a promise in exchange for the act of performance by the other party.A unilateral contact denotes a mechanical constraint which prevents penetration between two bodies .These bodies may be rigid or flexible.A unilateral contact is usually associated with a gap function which measures the distance between the two bodies and a contact force.An example of a unilateral contract is an insurance policy contract, which is usually partially unilateral. In a unilateral contract, the offeror is the only party with a contractual obligationA unilateral offer can occur where one party, the offeror, promise to pay for the performance of another, that is, a conditional promise. Promises in unilateral offer can perform in many ways. The acceptance of the unilateral offer takes place when the offeree performs the act in specific way.

Ineed the options .