6.4. Find all prime number solutions $(x, y, z)$ for the equation $19 x - y z = 1995$.

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6.4. From $y z=19 x-1995=19(x-105)$, and both $y$ and $z$ are prime numbers, so one of them must be 19, and the other is $x-105$. Let $y=19, z=x-105$. Thus, either $x$ or $z$ is even. Since they are both prime numbers, we have $x=107, z=2$. For the case where $z=19, y=x-105$, a similar discussion can be made.

In summary, the original equation has 2 sets of prime number solutions $(x, y, z)$: $(107,19,2),(107,2,19)$.