Answer:
C. Andrew was already obligated to paint the house. He gives no additional consideration in return for Rosalene's promise to pay more money.
Step-by-step explanation:
In this scenario Andrew had already agreed to do the painting for $500, so he is obligated to do the job or breach the contract.
He does not have a legal backing to make a counter deal in the middle of the job.
If Roseline decides to pay an extra $100 she does so without any obligations. She may or may not pay and Andrew is still obligated to complete the work.