(a) A number is divisible by 9 if sum of its digits is divisible by 9.

Sum of digits 0f 672 = 6 + 7 + 2 = 15

15 is not divisible by 9

Hence 672 is not divisible by 9.

(b) A number is divisible by 9 if sum of its digits is divisible by 9.

Sum of digits 0f 5652 = 5 + 6 + 5 + 2 = 18

18 is divisible by 9

Hence, 5652 is divisible by 9.