A fruit grower can use two types of fertilzer in his garden, brand P and brand Q. The amounts ( in kg ) of nitrogen , phosphoric, potash and chlorine in a bag of each brand are given in the table. Tests indicate that the garden needs atleast 240 kg of phosphoric acid, at least 270 kg of potash and at most 310 kg of chlorine. If the grower wants to minimise the amount of nitrogen added to the garden, how many bags of each brand should he use? What is the minimum amount of nitrogen added in the garden? What steps do you advice to a farmer to avoid overuse of fertilizers.