tax = (tax rate)*(charge before tax)
(total bill) = tax + (charge before tax)
or
(charge before tax) = (total bill) - tax
Then
(total bill) = (tax rate)*(charge before tax) +(charge before tax)
(total bill) = (charge before tax)*(1 +(tax rate))
(total bill) = ((total bill) -tax)*(1 + (tax rate))
Solving for tax rate, we get
.. (tax rate) = (total bill)/((total bill) - tax) -1
.. tax rate = (24.50)/((24.50) -1.50) -1
.. = 24.50/23.00 -1
.. ≈ 0.065217
.. = 6.5217%
The tax rate is about 6.5%.