(i) the current chargeable amount and

(ii) the advance surtax payable by it on the amount specified in (i) above calculated in the, manner laid down in sub- section (3), and shall pay such amount of advance surtax,-

(I) in a case falling under clause (a), as accords with the statement in equal instalments on the dates applicable in its case under sub- section (4); and

(II) in a case falling under clause (b), as accords with the estimate in equal instalments on such of the dates applicable in its case as have not expired, or in one sum if only the last of such dates has not expired.