Retrieve Value Of One Column In A Table?

Here is my problem:I have 2 tables Accounts and Transaction Logs.in Accounts table, it has column "Amount" which is a base amount of an account.and in Trans Logs table, it also has column "Amount" which is additional (add or minus to the base amount) amount of the account.and I don't know how to retrieve that base amount to edit it, then save it back to the table.That means I need to get a value of the right column by using Acc_No to find. I'm using DataSet, by the way.i think it should go like this:

Dim Amount as Decimal
Amount = *the code to retrieve the base amount*
Amount = Amount + txtAmount.Text
*the code to save the new amount back to Accounts table*