Tully Sales uses a periodic inventory system with the weighted average method of cost assignment. The following data are available. Date Jan. 6 Beginning inventory 400 15 26 31 Purchase 800 Purchase 1000 2200 Sale 1400 Closing inventory 800 Units Unit cost $ $5.50 $6.50 $8.00 The cost of sales for January is: (calculate your answer to the nearest whole dollar). O $7000. O $8 000. O $9 800. O $15 400.