Answer: Office of Management and Budget (OMB)
Step-by-step explanation
The Office of Management and Budget is the biggest office that is within the Executive Office of the United States President. The Office of Management and Budget is also a member of the President's Executive Office and the main function of the Office of Management and Budget is to help the United States president in budget preparation.
It should also be noted that the office helps in overseeing and monitoring federal agencies performance.