The question of whether a number is a multiple of 9 can be answered by summing its digits. In this case, the sum is 1+2+7 = 10, then 1+0 = 1. Because the sum is not 9, the number is not a multiple of 9.
This same trick is good for finding divisibility by 3 and 6. If the sum of the digits is a multiple of 3, then the number is a multiple of 3. If the number is both even and a multiple of 3, then it is a multiple of 6.
Example: 132 is divisible by 6, because it is even (ends in 2) and it is divisible by 3 (sum of digits is 1+3+2=6, which is divisible by 3).
This same trick is good for finding divisibility by 3 and 6. If the sum of the digits is a multiple of 3, then the number is a multiple of 3. If the number is both even and a multiple of 3, then it is a multiple of 6.
Example: 132 is divisible by 6, because it is even (ends in 2) and it is divisible by 3 (sum of digits is 1+3+2=6, which is divisible by 3).
