Because I bought 1 kg brown sugar and sugar, I used 6. 1 yuan.

Now, we change 1 kg of white sugar into 2 kg of brown sugar, that is, we buy 3 kg of brown sugar, but we have to pay more 1.4 yuan than 6. 1 yuan, that is, we have to pay more 7.5 yuan. In other words, I bought 3 kilograms of brown sugar to pay 7.5 yuan.

So 2.5 yuan per kilogram of brown sugar and 3.6 yuan per kilogram of white sugar.

(6. 1+ 1.4)÷3=2.5

6. 1-2.5=3.6

A: 2.5 yuan per kilogram of brown sugar and 3.6 yuan per kilogram of white sugar.