The cost of petrol X is Rs.6 per litre while petrol Y is only half as expensive. Find the cost of filling \[\frac{1}{3}\] of a cubical tank with petrol X and the rest of the tank with petrol Y if each side of the cubical tank is 20 cm long.

• A.  Rs. 16                  
• B.         Rs. 32                  
• C.  Rs. 40                  
• D.         Rs. 72