All lump sum compound interest equations consist of what four variables? To solve for one variable, how many others must we know?

How can we use the IRR to make an investment decision?

If the required rate increases, does the present value increase or decrease (assuming all else remains the same)?

Assuming the same interest rate, amount borrowed, and amortization period, which compounding (payment) period - monthly or annually - would result in less interest being paid by the borrower? Why?