Fastnet Sail Solutions plc manufactures and distributes sailing equipment. Its year$-$end is $31$ March. You are an audit manager in Forde & Co and are currently planning the year$-$end audit of Fastnet. You are reviewing the notes of a recent meeting between the audit partner and the finance director where two items were addressed:

Fastnet have a policy of revaluing land and buildings every three years. During the current year an external valuer was appointed to revalue a number of properties, including a recently acquired shipyard and drydock. The finance director has advised that the revaluation gain was $11\mathrm{.}7m.$ All documentation has been sent via email to the finance director; the physical paperwork remains outstanding. Also during the year, a review of plant and equipment used in the marine hardware division was undertaken and surplus plant was sold, resulting in a profit on disposal of $2m.$

Fastnet has recently reduced the size of its purchasing department and is pursuing a strategy of becoming a paperless organisation. This has resulted in the implementation of a new electronic purchasing system that requires all supplier documentation to be transferred from the supplier electronically or scanned into the system. All paper$-$based monthly supplier statements received from Fastnet's main suppliers have been photocopied and retained; however, these statements have not yet been scanned into the system nor reconciled to the payables ledger as at $31$ March $2024.$ The directors have provided you with an oral representation confirming that the payables balance of $25\mathrm{.}2m$ as per the draft financial statements is correct.

Required:

$($a$)$ Identify and explain the financial statement assertions relevant to the audit of the property, plant and equipment $($PPE$)$ and payables figures in the accounts of Fastnet for the year ended $31$ March $2024.$ For each assertion for each figure, describe substantive procedures you would perform to obtain sufficient and appropriate audit evidence.

$($b$)$ Explain what constitutes 'sufficient and appropriate' audit evidence and discuss the factors that are likely to have an impact on the reliability of audit evidence in the case of Fastnet's PPE and accounts payable.