She can feed her plants with 2 bags of soil for 3 months
Here, we want to calculate the number of months it will take for the plants to be fed with 2 bags of soil
From the question, 6 bags fed her plants for 9 months
Thus, the number of months it will take 1 bag to feed her plants will be 9/6 = 1 1/2 months
So if 1 bag can feed her plants for 1 1/2 months
Then two bags will feed her plants for 1 1/2 * 2 = 3 months