How did I know the inflows of new machine investment when I know annual cash operating cost, costs, useful-life, with depreciation straight line, tax 40%, and expected return 16%?

I don't see where there's any inflows of cash at all. Where do you see inflows? It has to be somewhere or they wouldn't be bothering with having you do the problem.

Figuring out a set of cash flows that includes depreciation can be a little tricky and you have to pay attention. You also have to understand that depreciation isn't a cash flow, but the extra expense affects taxable income, and therefore taxes, and the taxes are a cash flow. And you also have to know how to figure out the depreciation.

And somewhere there has to be inflows, though there can be outflows to go with it. I know you have to have more info, so there's no way to know how involved this might be. This isn't the easiest subject to just "give a hint" on.

Here's a link with some info but I don't know how useful it'll be, but you need to try to work something of this out yourself and then get help with whatever you don't understand.
Principles of Accounting Chapter 24 (http://www.principlesofaccounting.com/chapter%2024.htm#CAPITAL%20EXPENDITURE%20DECISIONS )