The question here tells you that n is one of the 7 numbers listed.
Statement 1 says that n is a multiple of 3. This means that n is equal to 3x1, 3x2, 3x3...etc. To match this rule up with the set in the question, simply check to see which of those 7 numbers are divisible by 3.
15 and 30 are the only two numbers that are divisible by 3. Since there are two possibilities, Statement 1 is not sufficient to answer the question, so Answer A and Answer D are incorrect.
Now look at Statement 2. Apply the same method as before with 2 instead of 3. Since n is a multiple of 2, find which numbers in the set are divisible by 2.
10, 20, 30, and 40 are all divisible by 2. Here, there are 4 possibilities, so Statement 2 is not sufficient to answer the question. Answer B is incorrect.
If you combine Statement 1 and Statement 2, 30 is a multiple of BOTH 2 and 3. Since it is the only number that is true when looking at both statements, Answer C is correct.
