If the item exchanged for the slave in the composite contract is a share subject to pre-emption (Shuf'ah), how is the right of pre-emption exercised?

Primary text

If the item exchanged for the slave is a share subject to Shuf'ah, the pre-emptor has the right of pre-emption. The pre-emptor takes the share by paying the portion of the one thousand that corresponds to the value of that share, as that value constitutes the consideration for the item.