A shopkeeper blends two varieties of tea, one costing Rs. 320 per kg and another costing Rs. 240 per kg, in the ratio 9 : 11. If he sells the mixture at Rs. 325.68 per kg, then his gain percentage is:
1
16.8%
2
18%
3
15.3%
4
More than one of the above
5
None of the above