Section 42

(1) Where a part of an asset is disposed or where some property
derived from an asset remains undisposed after a disposal of the asset –
(a) the acquisition cost of the assets, together with any expenditure wholly
and exclusively incurred for the purpose of enhancing the value of the asset;
or
First (b) the residue, in the case of assets used for trade or business on which
Schedule capital allowance have been made in accordance with the First Schedule to
this Act,
shall be apportioned between the disposed part and the undisposed part.
(2) Apportionment shall be made by reference to –
(a) the amount or value of the consideration for the disposal on the one
hand, referred to as "A"; and
(b) the market value of the property which remains undisposed on the
other hand referred to as "B".
(3) The acquisition cost or residue of the disposed part shall be apportioned
by applying the fraction A/(A+B), and the remainder shall be attributed to the
part which remains undisposed.
(4) Where a portion of interest or right in a chargeable asset is disposed,
and some part of that asset or any description of property derived from the
asset remains undisposed, the cost of acquisition in addition to any incidental
cost of the acquisition, or residue of the asset, shall be apportioned based on
the value of the sale compared to the market value of the undisposed portion.