Can you repace the question mark with the correct letter?
6 + 6 + 6 = N
7 + 7 + 7 = E
8 + 8 + 8 = R
0 + 0 + 0 = ?

O

6 + 6 + 6 = N (last letter of sum i.e. eighteen)
7 + 7 + 7 = E (last letter of sum i.e twentyone)
8 + 8 + 8 = R(last letter of sum i.e twentyfour)
Therfore
0 + 0 + 0 = O (last letter of sum i.e. zero)

Discussion