A certain gas obeys $$P(V_m - b) = RT$$. The value of $$\left(\frac{\partial Z}{\partial P}\right)_T$$ is $$\frac{xb}{RT}$$. The value of $$x$$ is ______ (Integer answer)
(Z : compressibility factor)

We are given the equation of state $$P(V_m - b) = RT$$, where $$V_m$$ is the molar volume and $$b$$ is a constant.

The compressibility factor is defined as $$Z = \frac{PV_m}{RT}$$.

From the given equation, $$PV_m - Pb = RT$$, so $$PV_m = RT + Pb$$.

Dividing both sides by $$RT$$:

$$Z = \frac{PV_m}{RT} = \frac{RT + Pb}{RT} = 1 + \frac{Pb}{RT}$$

Now we differentiate $$Z$$ with respect to $$P$$ at constant temperature:

$$\left(\frac{\partial Z}{\partial P}\right)_T = \frac{b}{RT}$$

Comparing with the given expression $$\frac{xb}{RT}$$, we get $$x = 1$$.

The answer is $$\boxed{1}$$.