Q:

Would you tell me about more about if I can use the phrase OF WHICH?

source text from cnn

This comprehensive solution would build on these initial measures and result in a final step for a period to be agreed upon and the resolution of concerns.

1) I am wondering about to what the preposition upon refers.
2) And, I think the verb agreed has two objectives, namely, the resolution and a period. Am I right?
3) Moreover, would anybody readily tell me the reason why the future tense has been applied in the past, and why the previous sentences have used the simple future?
4) Furthermore, would somebody please tell me if we can rewrite especially the last part of my original sentence, using the expression of which?
5) And finally, could anyone please elaborate whether or not I have grammatically and properly written my questions (interrogative sentences)? 

Thanks in advance.

A:

Well, you ask a lot of question in one, but let's see how far I get :)

1) Upon refers to a period. One of the things the solution would result in is a period, and (the length of) that period is something that needs to be agreed upon. In other words, no period is decide yet, but a decision should be made.
2) No. The sentence talks about "a comprehensive solution". That solution is builds on initial measures. That solution will then result in a final step that consists of two parts: a period of time during which this solution will be in place (that is the period to be agreed upon), and a resolution of concerns. A resolution of concerns means that current concerns (worries) will have to be taken away (resolved).
3) There is no past tense, actually. I assume you think that would build is past tense, but it is actually future: the would indicates a (likely) possibility in the future (if and when a final solution will be reached). Compare to "I'm thinking about buying a car. It would be a red one with four wheels." This doesn't mean I bought a car in the past or that it was red in the past. It means that if and when I buy a car, I expect it to be a red one. And I expect it to have four wheels.
4) I am not sure how or why you want to use of which, but you could write "This comprehensive solution would build on these initial measures and result in a final step for a period of which the length needs to be decided and the resolution of concerns."
5) I took the liberty of editing your question, and I fixed some wordings and turns-of-phrase. If you look in the edit history, I think your question on this is answered.

