Sandra sold 500 shares of Wren Corporation to Bob, her brother. She had paid $20,000 for the stock. Calculate Sandra's and Bob's gain or loss under the following circumstances.

I) Sandra sold the shares to Bob for $18,000. Bob sold them for $17,000.

II) Sandra sold the shares to Bob for $25,000. Bob sold them for $23,000.

III) Sandra sold the shares to Bob for $18,000. Bob sold them for $21,000.