Origanal price; 0.75
discount; ?
sale price; 015
discount with work i need to know how to find it

Since, no amount was given.

Finding original price using discount price and discount rate

Original price = Discount price divide by discount rate

Assuming Discount price is 20 and discount is 0.75
Original price = 20 / 0.75
Original price = 26.67

Sales price = Original price times net of 100% and sales discount in percentage

Assuming Original price is 100 ; 15% discount
Sales price = 100 x (1 - 0.15) = 100 x 0.85 = 85

or

Sales price = Original Price minus Original price times discount
                   = 100 - (100 x 0.15)
                   = 100 - 15
Sales price = 85

Use a calculator basically