correct answer was 24 years

Solution :

Let us take $A's$ age as $'x' ,B's$ age as $'y'$ and $C's$ age as $'z'$.

Given: Average age of $A$ and $B$ is $18$ years.

So, $( x + y )/ 2 = 18$

$x + y = 18 × 2$

$x + y = 36 -----------> 1$

After $3$ years, $A's$ age will be $'(x + 3)' ,B's$ age will be $'(y + 3)' $

Now the average age of $A,B$ and $C$ is $22$

So, $( x + 3 + y + 3 + z) / 3 = 22$

$( x + 3 + y + 3 + z)  = 22 × 3$

$x + y + z + 6  = 66$

$x + y + z = 66 - 6$

$x + y + z = 60$

Substituting equation 1 we get

$36 + z = 60$

$z = 60 - 36$

$z = 24$

So, C's age is $24$ years 

The correct option is 3).24 years