With any Percentage that the original price has already been affected. How to go backwards, You take the percentage value and subtract 100 from it. Then you take the 'Affected Regular Price' and you multiply that by 100. After that it's the 'Affected Regular Price Result' Divided by the 'Percentage Value' that will give you the answer of the 'Original price'.
Per say:
'Percentage Value: 29%' - 100 = 71
Affected Regular Price: $355 * 100 = 35 500
You divide: 35 500 / 71 = 500
Result: $500 is your 'Original Price'
