12 will be opposite to 24. Then the number of the people are sitting at the table will be 24.
<h3>What is Algebra?</h3>
The analysis of mathematical representations is algebra, and the handling of those symbols is logic.
The several people are sitting evenly spaced around a circular table and the positions are labelled 1, 2, 3 and so on.
The people at positions 3 and 15 are directly opposite each other.
Then the number of the people are sitting at the table will be 
1 is opposite to 13
2 is opposite to 14
3 is opposite to 15
Similarly, 12 will be opposite to 24.
Then the number of the people are sitting at the table will be 24.
More about the Algebra link is given below.
brainly.com/question/953809
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It is important to clearly understand all the important information's already given in the question. Based on those details the answer to the question can be easily determined.
In 17 hours the number of golf balls hit by Bill = 323
Then
In 1 hour the number of golf balls hit by Bill = (323/17) * 1
                                                                     = 19
So
The number of golf balls hit by Bill in 23 hours = 23 * 19
                                                                          = 437
So 437 balls will be hit by Bill in 23 hours. I hope the procedure is clear enough for you to understand. This procedure will help you to solve similar problems in future without requiring any outside help.