Small archive for the Apple MacBook Pro A1278, J30 platform, logic board 820-3115, with a trailing 3 in the name that may denote a revision or part. At 176 KB it is likely a boardview or a small firmware file, though the name does not state which. Apple 820-xxxx numbers identify the logic board and are printed on the PCB, so check them before use. Such files help locate components, trace power rails and verify test points during repair.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @fixtronix. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.
7-ZipWinRARThe Unarchiver (macOS)