here in Hydraulic system the pressure on both sides will remain the same
[tex]P_1 = P_2[/tex]
[tex]\frac{F_1}{A_1} = \frac{F_2}{A_2}[/tex]
[tex]\frac{mg}{\pi*\frac{10^2}{4}} = \frac{Mg}{\pi \frac{d^2}{4}}[/tex]
[tex]\frac{25}{10^2} = \frac{1900}{d^2}[/tex]
[tex]d = 87.2 cm[/tex]
so its diameter is 87.2 cm