For this case we must find the unit cost of the dresses Sara bought taking into account that I spend a total of $ 80.34. To do this, we must divide the total cost by 3.
Let the variable "x" be the unit cost for each dress.
You treat it as 10^4 (the small number is the number of zeros. Therefore the answer is 10000. Or of you meant 10^-4. Its the same concept, just reversed. So the answer in this case is 0.0004.