For A, with 3 tosses,
odd=odd+even=(odd+even)+even, or odd+(odd+odd).
We must add two even numbers and an odd or three odd numbers.
Therefore the answer is .
These can then be calculated.
three 1 to 6 digits sum to 13....
If the 1st digit is 1, the next two must both be 6....
If the 1st digit is 2, the next two must be 6,5 or 5,6..
If the 1st digit is 3, the next two must be 6,4, or 5,5 or 4,6.
With each step, there is an extra solution.
Hence the number of combinations adding to 13 is 1+2+3+4+5+6=21
Then the answer can be calculated.