Using formula data to create another formula

Using formula data to create another formula

Hi.. thanks for reading and hopefully pointing me in the correct direction.

I have a simple formula with a field name of "Actual Buy Price $"

The fields include: Regular Buy Price and Discount

The expression: (Regular_Buy_Price  -  Discount)

This works fine and as intended. 

What is needed now is a conversion inserted into a different field named "Actual Buy Price ₱" based on the result that is displayed in the field "Actual Buy Price $".

Basically I need to multiply the result from expression (Regular_Buy_Price  -  Discount) that is populated in the "Actual Buy Price $" with another field that reflects the current exchange rate named "USD/PHP Exchange Rate".

Thank you!