Concept: The question tests on Age problem
Solution:
Let Tom's age = x
Then Nicks age = 3x
Harry's age = 2 * 3x = 6x
Average age of all 3 = (x + 3x + 6x)/3 = 10x/3
Nicks age is 1 year less than the average age, i.e 3x = 10x/3 - 1
9x = 10x - 3
x = 3
Harry's age = 6x = 6 *3 = 18
Option B