We know that 1, 2, 3, 4, and 5 are left. Let's start with the max and work our way down.
Can 5 work? No, it can't because of the rules in this game.
1) 1 - >/3 1 - >/5
2) 4 - >/2 4 - >/5
The 'not both' rules ensure that there's no way the remaining 5 pieces can all be in. Also, remember that if 5 switches are in, then the 5 switch must be on (the last rule of the game says the switch whose number corresponds to the circuit load of the panel is itself on)
What about 4 switches? Well, we know 4 would have to be in. If 4 is in, then 2 and 5 are out, so at most 4 could take 1 and 3 with it, so 4 isn't going to work.
What about 3? If 3 is in, then 1 is out with 6 and 7. We could put 2 and 5 in 2 with 3 and have 4 out, and this would work.
In Out 3 6 2 7 5 1 4
This means that 3 is the maximum circuit load if 6 and 7 are out, so (C) is the correct answer choice.
Does this make sense? Let us know if you have any other questions!