Tech Innovations Inc., a technology manufacturing company, is considering the purchase of a new piece of machinery to enhance its production capabilities. The machine under consideration costs $500,000 and is anticipated to have a useful life of 8 years. At the end of its useful life, it's expected to have a residual value of $50,000. The company estimates that the new machine will enable it to increase annual production by 10,000 units. Each unit sells for $100 in the current market.

Tech Innovations Inc. incurs variable costs of $40 per unit and fixed costs of $200,000 annually. The company's tax rate is 30%.

a) Calculate the annual depreciation expense using the straight-line method.

b) Determine the annual net income increase resulting from the increased production if the company decides to purchase the new machine.

c) Evaluate the payback period for the investment in the new machinery, assuming no cash flows beyond the payback period.

d) Assess the accounting rate of return (ARR) of the investment in the new machinery, based on the average investment and average annual accounting profit over the useful life of the machine.