7The loss on account of rates of the common council of the City of London and of a metropolitan borough council shall be determined in accordance with the foregoing rules, subject to the following modifications :—
(a)the expenditure to be estimated and certified shall be the expenditure of the council in respect of the standard year falling to be borne by rates;
(b)the loss of the council on account of rates shall be the aggregate of the losses on account of rates levied in respect of the expenditure of the council in the several separately rated areas within the city or metropolitan borough.