Please help me with this question

Dear Student
Volume of water displaced by solid (metal bob) = 90 -50 = 40 mL.
As 1 mL = 1cm³
So in CGS system volume of bob is 40 cm³
$$\begin{gathered} 1c{m}^3 = {10}^{-6} m^3 \\ So \\ 40 c{m}^3 =40\times {10}^{-6} m^3 \\ So \\ in SI systtem volume of metal bob is 40\times {10}^{-6} m^3 \end{gathered}$$

Regards