Plz ! whats the cost to the store cost to store: ? markup: 80% selling price: 100.80

If I am correct, you are saying what was the price before 80%. If so, then you will want to multiply .8(100.8)= 80.64. Then, you will want to subtract that from the given price= 100.8-80.64=20.16.

If you are saying what is the price when brought up by 80%, then you will multiply as before. .8(100.8)= 80.64. Then you will want to add them together. 100.8+80.64=181.44

Does that help?