In the formula, X=3YZ² , X and Z have dimensions of capacitance and magnetic induction. The dimensions of Y in MKSQ system are 

According to question, [ X] = Dimensions of capacitance = [M^-1L^-2T²Q²] 
and [ Z] = Dimensions of magnetic induction. = [ML^-1Q^-1]
Given, X = 3YZ², 
$$\begin{gathered} \therefore \left[\mathrm{Y}\right]=\frac{\left[\mathrm{X}\right]}{\left[{\mathrm{Z}}^2\right]} \\ \Rightarrow \left[\mathrm{Y}\right]=\frac{\left[{\mathrm{M}}^{-1}{\mathrm{L}}^{-2}{\mathrm{T}}^2{\mathrm{Q}}^2\right]}{\left[{\mathrm{M}}^2{\mathrm{T}}^{-2}{\mathrm{Q}}^{-2}\right]}=\left[{\mathrm{M}}^{-3}{\mathrm{L}}^{-2}{\mathrm{T}}^4{\mathrm{Q}}^4\right] \end{gathered}$$