Business Law – 3 questions involving 3 different scenarios

I need help answering the following three questions:

1.  Steve buys a house from Jim. There is no written contract. However, Steve pays the purchase price, moves onto the property, and begins to build a new garage. Jim seeks to evict Steve from the property stating that there was never a valid contract. Is Jim likely to succeed? Why or why not?

2. Tony contracts with Paulie for Paulie to build him a house. They contract for a particular brand of pipes to be used. However, Paulie decides to use a slightly cheaper brand that is of a slightly lesser quality. Tony claims that this breach of the contract allows him to avoid the contract. Is he correct?

3. Frida agrees to sell a car to Johnny for $900. However, Johnny reneges on the written contract. Frida is able to find another buyer for the car at $700. What damages may she recover from Johnny?