What (a) is the basis on which (i) the Passenger Rail Agency of South Africa (Prasa) and (ii) Metrorail are renting diesel locomotives from Transnet, (b) number of Transnet locomotives have been in use under the specified rental, lease and/or loan agreement conditions in the past 36 months and (c) operational costs on the Transnet locomotives were carried by (i) Prasa and (ii) Metrorail during the past 36 months?