Three years ago, the average age of X and Y was 18 years. With X joining them, this average age became 22 years. What was the age of ‘Z’ ?

The age of Z is $64 – 42 = 22$ years.

Option (a) is incorrect because 30 years is the sum of the ages of X and Y three years ago, not their current ages.

Option (c) is incorrect because 29 years is the sum of the ages of X, Y, and Z three years ago, not their current ages.

Option (d) is incorrect because 29.5 years is not an integer.