Answer: a. Johnson will lose based on the theory of preexisting duty.
Step-by-step explanation:
Based on the information given in the question, Johnson will lose based on the theory of preexisting duty.
According to the theory of preexisting duty, when an individual is under the pre-existing duty to perform ans.auch person is under a contract, there will not be any consideration when there's a modification of the contract and then the modification is void.
In this case, it is the duty of Johnson to save lives as a firefighter. Therefore, saving the daughter of Bob simply means that he's performing his duty and if Bob refuses to pay him, Johnson will lose based on the theory of preexisting duty.