I got code XXX 542 , where find XXX ?

[wergilio]

where i must find code 374 ?
the full code is 374 542

[Mindcrime]

I know this is far past the date on which this question was asked, but in case anyone else is wondering...

In the building on the island, go into the basement. In the basement, there is a chest to the right of the fan. Once you open the chest, you will see two masks and a circular net. The first 3 digits of the code are on the mask on the left side (look at the bottom-right portion of that mask). When you find it, the main character will say she should remember the number, and she will then record the picture in her journal.