Sums between 5 and 12 or possible. This 8 total possible sums.
We have the option of 4, 5, or 6 for the one card we choose.
We also have the option of 1, 2, 3, 4, 5, or 6.
If we take the lowest option of each we get 4+1=5
If we take the highest totals of each option, we get 6+6=12.
Each value in between are also possible.