It's probably not the most efficient, but this is how I would initially attempt to work it out:
I think of the cable and the city is effectively 2 resistors in series creating a voltage divider. We need to isolate just the cable side to figure out #1.
First I divide the amount of power by the voltage to get the current through the system.
10E10 / 110 = 90,909,091 amps
The resistances, being in series, will have the same current through both. We can now either figure out the power lost in the cable with I^2*R.
90,909,091^2 * 5x10E-8 = 413,223,141 watts
We can then divide the 10E10 by the above, to get number of feet = 24.2