7698x138y is divisible by 72 72=8×9. So, if the number is divisible by 8 and 9 both, the number is divisible by 72 . Divisibility of 8 , Last 3 digit of number is divisible by 8 ,
38y
8
If we put y=4 the number 384 will divisibley by 8 . Divisibility of 9 , If sum of digit is divisible by 9 ⇒7+6+9+8+x+1+3+8+4 =
46+x
9
Put x=8 we get, the number 54 will divisible by 9 . x=8,y=4. ∴√4x+y=√4×8+4=√36=6