98. For what integer values of $x$ is the number $a\left(x^{3}+a^{2} x^{2}+\right.$ $\left.+a^{2}-1\right)$ divisible by 6 for any integer $a$?

As is known, the difference $a^{n}-b^{n}$ is divisible by $a-b$ for any natural number $n$; $a^{n}-b^{n}$ is divisible by $a+b$ for even $n$; $a^{n}+b^{n}$ is divisible by $a+b$ for odd $n$.

Prove the following statements (Nos. 99 - 127):
98. $x=3 t$ and $x=3 t-a^{2}$.