A three$-$phase $200$ MVA, $220/66$ kV transformer is connected in star on the high voltage side

and in delta on the low voltage side. The transformer winding resistances are $2\mathrm{.}5$ and $0\mathrm{.}2$

$,$ and the leakage reactances are $10$ and $1\mathrm{.}2$ for the high voltage side and low voltage

side respectively.

Calculate the per$-$unit impedance of the transformer refereed to the

$($a$)$ High voltage side.

$($b$)$ Low voltage side.