(b)where the sum is payable in perpetuity or for an indefinite time not terminable with any life in being at the date of such instrument [x x x] [Omitted by Act 12 of 1975 w.e.f. 1.5.1975]-the total amount which, according to the terms of such instrument [x x x] [Omitted by Act 12 of 1975 w.e.f. 1.5.1975] will or may be payable during the period of twenty years calculated from the date on which the first payment becomes due; and
