how many times can a combined 6 be rolled with two standard dice

6 by 6 matrix of possibilities

but
5 and 1 is the same as 1 and 5 for example
so really not 36 possible results but only the diagonal and those below (or those above)
so
6 + 5 + 4 + 3 + 2 + 1 = 21 possible combinations
of which
3 add to 6
(they are (3,3)(2,4)(5,1) )
so THREE unless you count ((4,2) and (1,5)) as different from ( (2,4) and (5,1) )