6. Given $a \cdot b \neq 1$, and $5 a^{2}+1995 a+8=0$ as well as $8 b^{2}$ $+1995 b+5=0$. Then $\frac{a}{b}=$ $\qquad$ .
6. $\frac{8}{5}$. (Hint: It is known that $a$ and $\frac{1}{b}$ are the roots of the equation $5 x^{2}+1995 x$ $+8=0$, apply Vieta's formulas. )