48 liters of milk is mixed with 'z' kg of impurity to form mixture 'A'. Another mixture 'B' contains milk and impurity in the ratio of 16 : 9 respectively. Mixture 'A' and 'B' are mixed in the ratio of 6 : 5 to form mixture 'C' in which the quantity of impurity becomes 37.5% that of milk then find the value of 'z'?