Answer:
at the beginning: 
when the plates are pulled apart: 
Explanation:
The capacitance of a parallel-plate capacitor is given by

where
k is the relative permittivity of the medium (for air, k=1, so we can omit it)
 is the permittivity of free space
 is the permittivity of free space
A is the area of the plates of the capacitor
d is the separation between the plates
In this problem, we have:
 is the area of the plates
 is the area of the plates
 is the separation between the plates at the beginning
 is the separation between the plates at the beginning
Substituting into the formula, we find

Later, the plates are pulled apart to  , so the capacitance becomes
, so the capacitance becomes
