How can I calculate the final price of the product as the price of a unity times its quantity in a group ? Magento 1

In my Magento store,a product has an attribute about the quantity of this product in a box,on the checkout is showing the price of the unity. How can I set its final price as the price of the unity times the quantity in a box ? (think as a box of shoes and it shows the price of the unity and the price of a box with many pairs, I want that the final price will be the box with many pairs inside)