Please Show step by step. Mainly stuck on problem 12 but would be great if you could help with the other two. Thanks in advance :)

Problem 10. Determine the payback period for an asset that has a first cost of $40,000, a salvage value of $8000 anytime within 10 years of its purchase, and generates income of $6000 per year. The required return is 7% per year. Problem i per year Find the present worth of a series of investments that starts at $1000 in year l and increases by 12% per year or 20 years. Assume the interest rate is 10% Problem 12. A construction company invested S60,000 in a new bulldozer. If the income from temporary leasin the length of time required to recover the investment at an interest rate of 16% per year is closest to g of the bulldozer is expected to be $15,000 per year