__Explanation__: As we can see that F + F gives F unit digit it is possible only when F = 0 So F has to be 0.

Now H + H + carry (if it is there) gives F as unit digit it is possible when H = 5 (we have max 9+9 = 18 so we will never have a carry equal to 2 so H + H = 10 is only possibility) Thus H has to be 5. A also is necessarily 1 because maximum carryover can be 1. C will have to be 2 because 1 is already taken now. And only number possible for B is 9 then to get 1 below. Thus we get:

9 5 1 1 G 0

1 5 J 0 K 0

1 1 0 G 2 1 0

Now possible J, G, K are 3 ,4, 7 or 6,7,4 or 7,8,3

1. A is 1

2. B IS 9

3. D can never be 7 because J,G or K are always 7

4. G cannot be represented by 6