A. Black & Co. Ltd owned two machines that had been purchased on 1 October 20X8 at a combined cost of £3,100 ex works. They were identical as regards size and capacity and had been erected and brought into use on 1 April 20X9. The cost of transporting the two machines to the factory of A. Black & Co. Ltd was £130 and further expenditure for the installation of the two machines had been incurred totalling £590 for the foundations, and £180 for erection.
Provision for depreciation using the straight-line method has been calculated from the date on which the machines started work, assuming a life of 10 years for the machines. The first charge against profits was made at the end of the financial year, 30 September 20X9.
One of the machines was sold on 31 March 20Y7 for £800 ex factory to H. Johnson. The work of dismantling the machine was undertaken by the staff of A. Black & Co. Ltd at a labour cost of £100. This machine was replaced on 1 May 20Y7, by one exactly similar in every way, which was purchased from R. Adams at a cost of £2,800, which covered delivery, erection on the site of the old machine, and the provision of adequate foundations. This new machine was brought into general operation on 1 July 20Y7.

Required
a. Show the journal entries that should be made on 31 March and 1 May 20Y7.
b. Show how you would arrive at the amount of the provision for depreciation as regards the three machines for the year ended 30 September 20Y7.