you can select one worksheet, then, holding down Ctrl select the rest
of the worksheets. now they are all grouped. whatever you do to one
worksheet will be done on all the other worksheets. so if your
columns all end *around* row 100, then in row 110 you could enter
=sum(a1:a109)
then drag it over to the right for the approximate number of columns
each worksheet has.
when you're done, select one different worksheet to ungroup them.
hope that helps.