HELP!!

My poor wife has two excel files and thinks she has about 24 hours of work
on her hands so I'm hoping someone here can help. What she has to do is
use the item number from a column in file A, and looking for the same item
number in file B. Then she needs to take a number from the same row but
another column and move it to a new column in file A. Any idea on how I
can do that? She has 200 pages worth to go through and I would hate for
her to have to look up each one individualy.

Thanks!