Explanation:

Correct option:4

When the couple married 5 years ago, their average age was 23.

So, their total age was =23 x 2 = 46 years.

Now, 5 years later, the total age of the husband and wife is =46 + 5 + 5 = 56 years.

The present average age of the husband, wife, and child is 20 years.

Therefore, their total age is =20 x 3 = 60  years.

 so the child’s age is =60 - 56 = 4 years.