Alice hired Doc to put in a swimming pool on her property for $10,000. Doc,prior to agreeing to build the pool,had taken a quick look at Alice's property and thought the condition of the land was optimal to dig out a pool.However, after he started digging, Doc found a subsurface of very hard rock that neither party expected.Doc told Alice that the discovery would require him to rent special equipment to remove the subsurface and would require an extra 12 hours of work. Doc told Alice it would cost and additional $5,000 to do the job right. Alice said she understood and agreed to give Doc the additional money.Doc spent the extra time and money and finished the job. Alice now wants to know if she is contractually responsible for the additional $5,000.

Is she? Explain.