Explanation

Carriage inwards is the cost of transporting purchased goods to your business. This is part of the cost of goods available for sale, so it goes in trading account.

Carriage outwards delivers goods to customers (selling expense). Discount allowed and rent are operating expenses. All three go to profit and loss account, not trading account.

Rule: Carriage inwards = buying cost (trading account). Carriage outwards = selling cost (profit and loss account).