Ramu sells milk after adulterating X litres of pure milk with 0.75 litres of tap water. If he sold milk after adulterating X litres of pure milk with 0.75 litres of mineral water instead, his profit would reduce by 15%.What is the cost of pure milk per litre? (The cost of mineral
water is Rs. 12 per litre and tap water comes for free. Ramu always sells at cost price.)