Alright so let's think there is a blank one that represents 0 and a 1,2,3,4,5, and 6 in all that's 7 different numbers.
For an example you don't have to do this for every number, but here's how the 0,s might work.
0,0 0,1 0,2 0,3 0,4 0,5 0,6
That is 7 different combinations for only one number but that is not the answer.
There are 7 numbers and 7 combinations.
7x7= 49
The answer is 49 dominos in each set. I feel like a teacher now but I hope this helped you
