The message in the response from the other tutor is that any next number will form a valid sequence, so "?" can be any number.
The general answer to ANY question like this is that there is no way to know what the "correct" answer is.
So questions like this must be considered as recreational puzzles -- not as formal math problems.
Take as much, or as little, time as you want looking for a relatively simple pattern that will generate the given sequence of numbers.
One strategy that often works is to view the given sequence as two (or more) spliced sequences. Using that strategy on this example gives a big hint as to what the expected answer is.
Given sequence...
1 3 5 7 13 12 25 18 __
Separated into two separate sequences...
1 5 13 25 __
3 7 12 18
Look for similar patterns in those two sequences to determine the logical next number in the first sequence....