A - Save Water Save Life

To address the situation of Water Scarcity in Chefland, Chef has started an awareness campaign to motivate people to use greywater for toilets, washing cars, gardening, and many other chores which don't require the use of freshwater. These activities presently consume $y$ liters of water every week per household and Chef thinks through this campaign he can help cut down the total usage to $\lfloor