Does anyone know how many units of each resource are traded with each trade agreement?

For example, I'm beginning with Rome and have 20 wine and 20 olive oil. The one trade agreement with Syracuse gives me 24 and 27 denarii (?) from each. I added two more trade agreements and now each of three give me 24/27 + tariff. I guess a reasonable answer would be 4 or 5 units are traded each time, as 20 is divisible by that, and upgrading the minor provinces gives 20 -> 40 of each resource.

Another question is how you can see the price of each resource, which could tie in to the previous question.

Finally, what happens if you get more trade agreements? Do the later ones not get the resource, or are the available resources split amongst them all now?