1SPECIALLY a part of my discussion with abhirup [ :P :P]
for solving (c) i took the following way....choose any two of the entries and then they will be at a distance of TWO if they have these two entries with values different form the original one!which can happen only in TWO ways for each of the two entries
SUPPORTING EXAMPLE:::
suppose we selected following TWO entries in the ternary sequence so we have:::
[0,1........................] as original sequence
now entries at distance TWO from above are
[1,0]
[1,2]
[2,0]
[2,2]
i.e. 2*2=4
so answer for the part (c) should be 10 C 2 * 2 * 2!