X Contracted with Z

Multiple Choice

X contracted with Z.X promised to pay $500; Z promised to build a cabinet to hold X's DVD's.The essential terms included the type and quality of the wood,the dimensions,and the date of completion-February 13,2011.The work went more easily than expected and Z said to X,"If you pay me another $85,I will have this finished and be out of here by February 10." X agreed.If the cabinet was done to specifications by the 10th,but X refused to pay anything,Z would be entitled in law to

A) nothing.
B) $500.
C) $585.
D) only $85.
E) a "fair price."