I'm doing a budget for work where I have to add $15\%$ to a price. But then my client is going to subtract $15\%$ from the total but I need to make the original price back. I.e.
$$£100.00 + 15\% = £115.00$$ $$£115.00 - 15\% = £97.75$$
My problem lies in that my client is unaware of the original number ($£100.00$) and I need to get this back as this is profit.