How do I open a file in VBA or a macro to open a file# that is entered into cell B1?

where ACCT is just a number refering an acct# which also
is the acct # and .xls
If B1 is 12345 then it opens 12345.xls, etc.(over 100 files
on the drive)

What I would need is something like...

ActiveCell.Range("B1").select
Let ACCT = ActiveCell
Workbooks.Open Filename:="C:\subdirectories\[ACCT].xls"
But I cannot find anything that will do something like this... (Is it possible? )

Many thanks!!
Robert