On Monday, Nell tells Outdoor Landscaping, Inc. that she will pay Outdoor five hundred dollars if a variety of tasks are completed by Friday. On Wednesday, when Outdoor is more than half done with the work, Nell says that she has changed her mind. These parties had:

$$ No contract.

$$ A unilateral contract as soon as Outdoor began to substantially perform the tasks.

$$ An expired contract when Nell said that she had changed her mind.

A bilateral contract as soon as Nell and Outdoor agreed upon the tasks to be performed by Outdoor and the amount to be paid by Nell.

$$ A quasi$-$contract when Nell said that she would pay for certain performed tasks.