A shopkeeper sells ladoos at Rs. 16.5 per kg and a 'ladoo' is made up of 'flour' and 'sugar' in a ratio of 7 : 1 respectively. If the price of 'flour' and 'sugar' is 1 : 4 (per kg) respectively and thus, he earns a profit of 50% then what is the cost price of 'sugar' per kg?