7.98 Two people are playing a math game. Player A selects a set of 1-digit integers $x_{1}, x_{2}, \cdots, x_{n}$ as the answer, which can be positive or negative. Player B can ask: what is the sum $a_{1} x_{1}+a_{2} x_{2}+\cdots+a_{n} x_{n}$? Here, $a_{1}, a_{2}, \cdots, a_{n}$ can be any set of numbers. Determine the minimum number of questions Player B needs to ask to guess the answer:
[Solution] When taking
$$
a_{j}=100^{j-1}, j=1,2, \cdots, n
$$

then, by asking just one question, we can determine $x_{1}, x_{2}, \cdots, x_{n}$.