Three types of nuts are mixed together. If the ratio of nuts costing Rs. 9 and Rs. 14 is 1 ∶ 1, while the ratio of nuts costing Rs. 14 & Rs. 20 is 5 ∶ x. Resultant price of mixed nuts is Rs. 12. If the quantity of mixed nuts of costing Rs. 14 is 7 gm, then find the quantity of nuts of costing Rs. 20.