Is 543 a composite number

Answer 1

Yes, it has divisors other that 1 and itself, e.g. 3,181. In fact by the divisibility condition, "The sum of the digits is divisible by 3, therefore the number itself is divisible by 3", clearly 543 is divisible by 3, i.e.

5+4+3 = 12/3 = 4 making it composite.

Answer 2

Yes.