The number of different words (eight-letter words) ending and...

EQUATION - 8 letters. Consonants - $\mathrm{Q}, \mathrm{T}, \mathrm{N}-3$ letters. first letter of $8-$ letter word can be any of 3 consonants Last letter of $8-$ letter word can be remaining 2 consonants. The middle $6-$ letters can be arranged in 6 ! ways. So, number of different words $=3 \times 2 \times 6$ ! $=6 \times 720=4320.$