Final answer:
George legally owes $125 to Bob for the racing bike modifications because Bob accepted George's offer of an additional $25 to ensure the bike would be finished on time, providing new consideration for the amended agreement.
Step-by-step explanation:
In the scenario presented, George legally owes $125 to Bob for the racing bike modifications. Initially, George and Bob entered into a contract for the modification of the bike for $100 with a set delivery date. However, upon expressing concern about the timely completion of the work, George agreed to pay an additional $25 so that Bob could pay for the overtime required to finish on time. This agreement for an additional $25 in exchange for Bob ensuring the bike is ready by the deadline constitutes a new consideration, which is why George owes the higher amount.
The correct answer would be option C: $125 because Bob gave consideration for George's promise to pay the additional $25. This takes into account that although Bob had a pre-existing duty to modify the bike, the new agreement for early completion and the payment for overtime work constitutes a modification of the original contract, supported by fresh consideration.