Answer:
Periodic system: FIFO ; COGS= $11400, closing inventory = $7700, gross profit=$14000. LIFO = closing stock= 6600, COGS=$12500, gross profit=12900.
perpetual system: FIFO ;COGS=11400, closing stock= $7700, gross profit= $11400. LIFO ; COGS=$12500, closing stock= $6600, gross profit = $12900
Reason for a higher gross profit in FIFO than LIFO is some of the stock ends up not being sold as they are maybe old, out-fashioned, and obviously new trend come about everyday. 
Step-by-step explanation:
 PERIODIC 
DR purchases account CR
11-Aug bank 9600 inventory 16100 
20-Aug bank 6500 
 
 16100  16100 
 FIFA cost of sales 
 
opening balance 3000 
purchases 16100 
closing 7700 
cost of sales  11400 
gross profit 14000 
sales 25400 
cost of sales 11400 
closing inventory 7700 
200 units from 11 aug 1200 
1000 units from 20 aug 6500 
 LIFO 
 closing balance 6600 
600 units from 01 aug 3000 
600 units from 11 aug 3600 
 Cost of sales 
opening stock 3000 
purchases 16100 
closing stock 6600 
cost of sales 12500 
 
gross profit 12900 
sales 25400 
cost of sales 12500 
perpetual inventory system 
 FIFA 
cost of sales 11400 
10-Aug 2000 
15-Aug 5800 
27-Aug 3600