Mary owns a small cattle farm with a fenced-in pasture. Her neighbor, Stephen, notices that there is a break in Mary's fence large enough for her cattle to push through. Without consulting with or telling Mary, Stephen repairs the break. Upon learning of the repair, Mary is grateful, and expresses her thanks to Stephen. However, Stephen is expecting to be paid for the repair.

a.What is Mary's best argument that she is not liable to Stephen for the repair?

b.What is Stephen's best argument that Mary is liable to Stephen?