Basically, offset is how far from the center the mounting hub on the rim is. The numbers are, unless I'm mistaken, given in millimeters. I don't quite know the range of offsets that an EJ8 can fit, but for a 7thgen, it's something like +35 to +44.
Dunno for sure, but you should be good with either the 38 or 40. I'll leave that to some 6thgen gurus we have lurking about to chime in and give their 2 cents