Dear Kalpana,

According to me, the answer to this problem should be 64.

If father is coded as 216, Father word has 6 letters and cube of 6 is 216.

Grandson, which contains 8 letters is coded as 512 and cube of 8 is 512.

so, Wife, it is a four letter word and cube of 4 is 64 so 64 must be the answer to this question.

Good Luck!