Extra Credit Assignment: The Guitar Lessons Bill decides that he wants to learn

Extra Credit Assignment: The Guitar Lessons
Bill decides that he wants to learn to play the guitar. He’s not good with instruments, so he wants someone to teach him. He’s also low on cash, so he’s hoping to get guitar lessons in exchange for a service. He puts signs up all around town that say:
“Wanted: Guitar Lessons. Beginning guitar student will mow your lawn in exchange for lessons. Prefer experienced teacher. Call Bill – 555-5555.”
Jessie sees Bill’s ad. She teaches guitar lessons to a few other students as well. She is currently paying a lawn service to mow her lawn and thinks this arrangement sounds like a good plan – she could drop the lawn service. She calls Bill and says, “sounds like a good plan. I’m in. Let’s start on Monday at 5 pm.”
Answer the following four questions for up to 5 extra credit points:
Is this contract oral or written?
Identify the offer, acceptance and consideration.
Is this contract enforceable?
Do you see any potential problems with this contract?