ASP.NET - Set Connection time out in the app settings section of the web.config file.

I have the following in my web.config file.
<appSettings>
</appSettings>

I want to be able to run code like the following in my application...

cmd = New SqlCommand(sqlStr, conn)
cmd.CommandTimeout = Convert.ToInt32(ConfigurationManager.AppSettings("ConnectionTimeout"))
cmd.Connection.Open()
cmd.ExecuteNonQuery()

how do I enter this into the web.config file correctly for say, 90 seconds?
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