Transmission line design

This is the problem: "A utility company just hired you as a new lead electrical engineer. They requested you to design a new 500_MW power station and transmission line to connect Sydney to Brisbane (1083 km). The transmission line is lowered to 11 kV before entering residential area and then, is connected to a delta-wye transformer before connecting to a residential area that has 50 residential households. Determine the rating (power, voltage) and turn ratio of the transformer ."

How can I know the input voltage, that is the value that the voltage assumes before being lowered to 11kV?

The question seems to be a universal one. 500 MW, 1000s Kms, Power stations, 50 House hold, then asking for details of the distribution Xmer. Something strange! Generally High Voltage and Low Voltages are dealt separately by separate organisations.