Lee contracts to paint Sally's two-story house for $2,500.

Lee contracts to paint Sally’s two-story house for $2,500.  Sally realizes that she will not have sufficient money, so she transfers her rights under this agreement to her neighbor Karen, who has a three-story house.  Karen notifies Lee that Sally’s contract has been assigned to her and demands that Lee paint Karen’s house for $2,500. 

Define assignment and explain if you feel Lee is required to paint Karen’s house.

If Lee agrees to the assignment but fails to perform the contract to paint Karen’s house, can Karen sue Sally for damages?