I recently received a payment from a customer for a past due bill. He paid $$4800$ which did not include the sales tax of $5\%.$ I called him up to let him know his mistake, but he informed me that when we had spoke originally, that my total bill would be $$4800,$ which included sales tax. Knowing that it is unlikely that I will get any additional money from this customer, I am going to pay the sales tax out of what I have collected. What I need to know is the Taxable Amount that I need to report, so that when I add on the Sales Tax, the total bill would be $$4800.$

One way to look at this would be:

Taxable Amount $+5\%$ Sales Tax on Taxable Amount $=4800$