Can someone please help me with this question?

A capacitor is formed by two concentric spheres whose radii are 25 cm and
12.5 cm respectively, with a liquid insulant between them with relative
permittivity 3. The potential difference between the spheres is 10 kV. Find (i)
the capacitance and (ii) the maximum field strength in the gap between the
two spheres

Do I use this formua : V = -∫Edr+constant

so, 10000 = q/2pi*eo*er * (1/25 - 1/12.5)

Is this correct?

 

ok, I worked out the capacitance:

∆ V = Q / (4πε0) ∫ (1/r^2) dr between the limis a to b

= Q / (4πε0) { 1/a - 1/b)

C = Q/∆ V = 4πε0) / (1/a - 1/b)

But with the max field strength do i use : q = cv

Then apply q to : E = q/4∏*εr*ε0*r^2

Is that correct?