The discount is 40% that means the discount is 40% off from the original price. Or we could write the discount as below.
discount = 40% × original price
Find the original price
original price = sale price + discount
original price = 36 + 40% original price
100% original price = 36 + 40% original price
100% original price - 40% original price = 36
60% original price = 36
0.6 original price = 36
original price = 36/0.6
original price = 60
The original price of the headphone is $60