I think their answer may be confusing you. The old transmission line impedance before the step up transformer was installed is 10< 30 on 13.2 KV
Now the transformer is installed so transmission line will see 132 KV
You calculate new impedance using the new voltage
Z new = Z old X (old voltage /New Voltage) ^2
The difference in impedance will be magnitude of (Z old - Z new) or vice versa. I think their answer showing some operation on Z old which was not needed. You keep Z old as it is, calculate Z new using the new voltage base. Power base is same in old case and new case, so you can ignore that. They got Z old and Z new little mixed up and confusing people.
