(4)Where, in exercise of the powers conferred by clause (b) or sub-clause (i) or sub-clause (ii) of clause (c) of sub-section (2) of section 68F, any existing permit is cancelled or the terms thereof are modified so as to prevent the holder of the permit from using any vehicle authorised to be used thereunder for the full period for which the permit would otherwise have been effective, the compensation payable to the holder of the permit for each vehicle affected by such cancellation or modification shall be computed as follows:-(a)for every complete month or part of a Two hundred month exceeding fifteen days of the rupees unexpired period of the permit:(b)for part of a month not exceeding fifteen One hundred days of the unexpired period of the rupees permit :Provided that the amount of compensation shall, in no case, be less than four hundred rupees.