Simple math question - solving for 3 vars

Ok, I think I’m just way too tired for this right now. :doh:

I’m trying to figure out this ultra-simple accounting question. I’ve substituted the charts of accounts for these three variables; i, j, k.

i + k = 424
k + j = 396
i - j = 28

How do you solve for these variables? Is it possible? Am I becoming dim? :hurt: