Also, F-T told us.

There are 20 independent senators with an "unfavourable" voting inclination.

If you look back at the rules of the game under "The Round - Keeping up to Date" you'll see a chart defining the ranges of voting inclinations. Unfavourable means that 21% to 40% of independent senators will vote in favor of the proposal.

21% of 20 is 4.2, but because that's the minimum, and because I don't think we have fractions of senators or of their votes, we must round it up to 5.

40% of 20 is 8. That is the maximum number of senators who will vote in favor of the proposal. We can subtract that from the total to get the minimum number of senators voting against the proposal. 20 - 8 = 12.

So we know for certain that there are 5 senators voting for the proposal and 12 voting against it. 5 + 12 is less than 20, and the difference between the two will give us the number of as yet undecided senators, 3.