Between the numbers 1221 2736 and 45 which of the numbers of visible by both 3 and 9

Among the given numbers, only 2736 and 45 are divisible by both 3 and 9.

Step-by-step explanation:

We know that an integer is divisible by 3 or 9 iff (if and only if) the sum of it's digits are divisible by 3 or 9 respectively.

Now,

sum of the digits of 1221 = (1 + 2 + 2 + 1) = 6 which is divisible by 3 but not divisible by 9, hence, 1221 is divisible by 3 but not by 9.

and,

sum of the digits of 2736 = (2 + 7 + 3 + 6) = 18 which is divisible by both 3 and 9, hence, 2736 is divisible by both 3 and 9.

and,

sum of the digits of 45 = (4 + 5) = 9 which is divisible by both 3 and 9, hence, 45 is divisible by both 3 and 9.