Suppose that there are $p$ people behind Kaukab. This means that there are $2p$ people ahead of her. Including Kaukab, the total number of people in line is $n = p + 2p + 1 = 3p + 1$, which is one more than a multiple of 3. Of the given choices $(23, 20, 24, 21, 25)$, the only one that is one more than a multiple of 3 is 25, which equals $3 \times 8 + 1$. Therefore, a possible value for $n$ is 25.