How do I calculate the amount of sales tax that is included in total receipts?

Say sales tax is 15%.

The formulae will be:   15/(100+15)

To calculate the sales tax that is included in a company's receipts from items subject to sales tax, divide the receipts by 1 + the sales tax rate. For example, if the sales tax rate is 6%, divide the total amount of receipts by 1.06. If the sales tax rate is 7.25%, divide the total receipts by 1.0725.

divide the receipts by 1 + the sales tax rate like

 if receipt 300 , sales rate  7%

sales tax=2/(1+7%)=1.869