A shop wants to sell a certain quantity of grains. it sells half of the quantity and an additional 3 kg of these grains to the first customer. then it sells half of the remaining quantity and an additional 3kg of these grains to the second customer. finally when the shop sells half of the remaining quantity and an additional weights 3 kgs of these grains to the third customer, there are no grains left. the initial quantity, in kgs of grains are