Answer:
The answer should be 3.
Explanation:
In order to come to this conclusion, it is important to factor both of the numbers 18 and 30.
It is important to list the prime factorization of both numbers.
18: 2 x 3 x 3
30: 3 x 2 x 5
The number must be odd as the question has stated, and it must be the largest number he could be thinking of.
Therefore, 3 is probably the answer.