Tom broke his leg. His neighbor and friend, Bruce, stopped by for a visit and said, $"$I$\text{'}$d like to offer to mow your lawn for you next Saturday." Tom accepted. This agreement is:

a$.$ enforceable, because there was an offer and acceptance.

b$.$ enforceable, because it is an implied$-$in$-$fact contract.

c$.$ unenforceable, because it is not in writing.

d$.$ unenforceable, because there is not legally sufficient consideration.