(a)the deduction under sub-clause (i) of clause (a) of section 30, in the case of rent, shall be such amount as the [Assessing Officer] [ Substituted by Act 4 of 1988, Section 2, for " Income-tax Officer" (w.e.f. 1.4.1988).] may determine having regard to the proportionate annual value of the part used for the purpose of the business or profession, and in the case of any sum paid for repairs, such sum as is proportionate to the part of the premises used for the purpose of the business or profession;