Answer
a) $\displaystyle C = 1.5*10^{-10}$ Farads
b) $\Delta V_{max} = 12$ kV
Work Step by Step
The capacitance for a dielectric-filled capacitor is $\displaystyle\quad C = \kappa\frac{A\epsilon_0}{d}$
In section 26, table 26.1 gives the dielectric constant for a variety of many different materials and it lists the dielectric constant for Teflon at 2.1.
Part a.)
To find the capacitance of the capacitor, use the equation listed above and plug in the given values
$\displaystyle C = (2.1)(\frac{(0.04)^2(8.85*10^{-12})}{0.0002}) \approx 1.5*10^{-10}$ Farads
Part b.)
Table 26.1 also gives the maximum electric field vector, $\vec{E}_{max}$, for Teflon at $60\cdot 10^6$V/m. To find the potential difference inside of a capacitor, we just have to multiply electric field by the capacitor's separation distance: $\Delta V_{max} = \vec{E}_{max}\cdot d$
$\Delta V_{max} = (60*10^6)(0.0002) = 12,000$ Volts
