(b)if the cost of the new asset is less than the ] [net consideration] [Substituted by Act 21 of 1979, Section 8, for certain words (w.e.f. 1.4.1979).][in respect of the original asset, so much of the capital gain as bears to the whole of the capital gain the same proportion as the cost of acquisition of the new asset bears to the ] [Inserted by Act 29 of 1977, Section 13 (w.e.f. 1.4.1978).] [net consideration] [Substituted by Act 21 of 1979, Section 8, for certain words (w.e.f. 1.4.1979).][shall not be charged under section 45:] [Inserted by Act 29 of 1977, Section 13 (w.e.f. 1.4.1978).]