Answer
$55cm$
Work Step by Step
We can find the required diameter as follows:
$p_{\circ}+\frac{m_1g}{r_1^2\pi}=p_{\circ}+\frac{4m_2g}{r_2^2\pi}+\rho gh$
This can be rearranged as:
$r_2^2=\frac{4m_2g}{\pi}\cdot\frac{1}{\frac{m_1g}{r_1^2\pi}-\rho gh}$
We plug in the known values to obtain:
$r_2^2=\frac{4(110)(9.8)}{\pi}.\frac{1}{\frac{(55)(9.8)}{(8)^2\pi}-(908)(9.8)(100cm)}=0.0766cm$
$\implies r_2=0.276cm$
$\implies d=2(0.276cm)=55cm$
