Mary agrees to sew Georgia's prom dress for $50 plus costs. Georgia decides that she wants ruffles around the neck and calls Mary who says it will now cost $60. When Mary finishes the dress (with ruffles), Georgia must pay:
a. $50, since that is the original agreement.
b. $50, since a modification must be in writing.
c. $60, since the modified agreement is supported by additional consideration.
d. $60, since any subsequent agreement is enforceable.