My friend has a business opportunity available to him. He says that if I invest with him I will receive $$1250$ a month for five years from the investment. I believe that for such a risky investment I need to get at least $15\%$ return. How much is the most I should be willing to give him?

$$52,543\mathrm{.}30$

If the investment is expected to last forever, how much is the most I should give him?

I need help with #$10.$