There are two types of fertilisers \( F_1 and F_2. F_1\) contain 10% nitrogen and 6% phosphoric acid and \( F_2\) consists of 5% of nitrogen and 10% phosphoric acid. After testing the soil conditions, a farmer finds that she needs atleast 14kg of phosphoric acid for the crop. If \( F_1 \) costs Rs.6/kg and \( F_2 \) costs Rs. 5/kg, determine how much of each type of fertilizer should be used so that nutrient requirements are met at a minimum cost. What is the minimum cost?