In order to find equal quantities to be mixed, we'll need to find equivalent ratios such that the SUMS of the terms are equal.
1 + 2 + 4 = 7
3 + 5 + 6 = 14

Take the ratio 1 : 2 : 4 and multiply all terms by 2 to get the equivalent ratio: 2 : 4 : 8
Notice that 2 + 4 + 8 = 14
So, in 14 units of the first mixture, there are 2 units of petrol, 4 units of diesel and 8 units of kerosene.
Similarly, 14 units of the second mixture, there are 3 units of petrol, 5 units of diesel and 6 units of kerosene.

When we combine 14 units of each mixture, we get 28 units in the ratio: (2 + 3) : (4 + 5) : (8 + 6), which simplifies to be 5 : 9 : 14

Answer: A