Answer:
b) a debit to the seller and credit to the buyer for $100
Explanation:
The portion of the utilities bill consumed by the seller is not to be borne by buyer Bill, he cannot be made to pay for what he did not consume, the correct treatment is for seller to bear the $100 consumed by him by way of the following entries
Debit The seller $100
Credit Buyer bill $100
This is in the spirit of fairness to both Buyer Bill and Seller.