Answer:
The correct answer is a) a pre-established formula
Explanation:
The pre-established formula in this case refers to the fixed salary that a worker earns, while a variable payment is a payment that is effective if a certain condition other than going to work is attained.
This structure of payment is very common for CEOs. CEOs usually have a fixed annual salary, and also a variable salary or bonus that depends on their performance (which is measured by the economic profit of the firm).