Answer
200 kV (2 significant figures).
Work Step by Step
The town requires 55 MW, and the efficiency is 98.5 percent, so the power at the generating plant was greater. That power was (55MW/0.985)=55.838MW.
Thus the power lost in the process of transmission is 0.838 MW.
The transformers are assumed to be perfect. The power loss is because of resistive heating in the transmission lines.
Calculate the current in the (two) transmission lines.
$$P=I^2R$$
$$I=\sqrt{\frac{P}{R}}=\sqrt{\frac{0.838\times10^6W}{2(56km)(0.10\Omega/km)}}=273.5A$$
Find the voltage needed to generate 55.838MW of power using that current.
$$V=\frac{P}{I}=\frac{55.838\times10^6W}{273.5A}\approx 200kV$$
The voltage is reported with 2 significant figures.
