You don't need to know anything about resistance. My answer is 100 watts. 20 amps flowing through the wires yields a drop of 5 volts. 20 x 5 = 100.
This depends on whether the load is 20a at 120v or 20a at 115v.I got 96 watts
115/120 = .96
2400 watts x .04= 96 watts
It's both. At the starting point, a 120V source is pushing 20 amps through both the load and the intervening wires. That 120V source is therefore supplying 120 x 20, or 2400 watts. At the other end, a 115V source is pushing 20 amps just through the load. That 115V source is therefore supplying 115 x 20, or 2300 watts. The energy lost in the wires is the difference, or 100 watts.This depends on whether the load is 20a at 120v or 20a at 115v.