Sequences And Series

Let \(a, b\) be two non-zero real numbers. If \(p\) and \(r\) are the roots of the equation \(x^{2}-8 \mathrm{a} x+2 \mathrm{a}=0\) and \(\mathrm{q}\) and s are the roots of the equation \(x^{2}+12 \mathrm{~b} x+6 \mathrm{~b}=0\), such that \(\frac{1}{\mathrm{p}}, \frac{1}{\mathrm{q}}, \frac{1}{\mathrm{r}}, \frac{1}{\mathrm{~s}}\) are in A.P., then \(\mathrm{a}^{-1}-\mathrm{b}^{-1}\) is equal to _____________.