Answer
$8.94\times 10^{-11}\;\rm F$
Work Step by Step
We know that the capacitance of a parallel plate capacitor is given by
$$C=\kappa C_0=\dfrac{\kappa \epsilon_0 A}{d} $$
where $\kappa$ is the dielectric constant.
The area of the capacitor is the area of the cell surface, which is the area of a sphere's surface, A=$4\pi R_{\rm cell}^2$.
$$C= \dfrac{ 4\pi \kappa_{\rm cell} \epsilon_0 R_{\rm cell}^2}{d} $$
Plug the known;
$$C=\dfrac{4\pi(9)(8.85\times 10^{-12})(25\times 10^{-6})^2}{(7\times 10^{-9})}$$
$$C=\color{red}{\bf 8.94\times 10^{-11}}\;\rm F$$
