Modify Excel File From Code

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ASP.NET

iam workin on asp.net 4 web site
i have some excel files uploaded on server
what i need to do depending on users entry
i make some modification on that excel file from code with out displaying the excel file
for example if user write in quantity filed 5
i go to excel file update cell b4 to 5
something like that

i try to work using Microsoft.Office.Interop.Excel
but the problem is the server that host my web site
no ms excel install on it
so how i can make modification on that file
waiting for any help