Question 1064965
The total number of ways are 6+5+4+3+2+1=21, as you had.
Rolling doubles are 6 ways, 3 of which are included in the 21 above. 11,22,33 are not included.
Therefore, you count half of the doubles and don't count the other half, so it is the second, or 2/3 (24/36).