fair market rental value (having regard to rent being charged for similar space including additional rent for Operating Expenses and Real Estate Taxes) of space used by the Landlord and/or its property manager, acting reasonably, in connection with the maintenance, repair, operation, administration and management of the Building and such fair market rental value of any building amenities (such as conference and day-care facilities provided primarily for tenants of the Building), together with the reasonable costs relating to such building amenities;