Answer:
The amount of milk remaining in the cartons = a - 250
Explanation:
The carton of milk was full . 250 millilitres of this milk were used for a cooking recipe. The millilitres of milk still remaining in the carton will be the actual millilitres of milk in the complete carton minus the 250 millilitres of milk used for the cooking recipe.
Let
amount of milk in the full carton = a millilitres (recall the question said the carton was filled with milk)
The amount of milk remaining in the cartons = amount of milk in the full cartons - 250 millilitres of milk used for cooking.
The amount of milk remaining in the cartons = a - 250