PQR Inc. plans to purchase new machinery costing ZAR 500,000 with an expected useful life of 6 years and a residual value of ZAR 50,000. The depreciation method is straight-line. The company's cost of capital is 15%. The projected cash flows and profits are:

Year	Cash Flow	Profit
1	R60,000	R10,000
2	R70,000	R15,000
3	R80,000	R20,000
4	R90,000	R25,000
5	R100,000	R30,000
6	R110,000	R35,000

Requirements: a) Discuss the concept of relevant costs in investment appraisal. b) Differentiate between the payback period and net present value (NPV). c) Calculate the following using the provided data: i) The payback period. ii) The NPV. iii) Provide a recommendation on whether PQR Inc. should invest in the new machinery.