For the first question: if there are 24 senators, two-thirds of 24 is 16 votes. For the second question: if four senators are unable to vote, the number does not automatically become 20. The Constitution refers to two-thirds of all the Members of the Senate, so the 24-member figure gives a threshold of 16 votes. Whether unavailable senators should be excluded is a matter of legal interpretation and must be decided by the proper authorities. Thank you!