Answer:
a) ending inventory:     11,850,000
    cost of goods sold: 25,200,000
   gross profit               25,200,000
b)
ending inventory:     1,800,000
cost of goods sold:  23,100,000
gross profit  50,400,000 - 23,100,000 =  27,300,000
Explanation:
5,200 at $600
 4,100 at $700
6,200 at $800
purchase 29,000 at $900
-sold 28,000 grills
As we use LIFO we sale from the last purchase thus, 29,000 - 28,000 = 1,000 of this units are added as another layer for the inventory account
<em><u>ending inventory</u></em>
5,200 at $  600
 4,100 at $   700
6,200 at $  800
1,000  at $  900
Total    $ 11,850,000
cost of good sold:
28,000 x $900 = $25,200,000
sales revenue
28,000 x 900 x 200% = $50,400,000
gross profit sales revenue less COGS
b) 5,200 at $600
 4,100 at $700 
6,200 at $800
<em>purchase 15,500 at $900 </em>
-sold 28,000 grills
we check how many layer deep we go:
28,000 - 15,500 at 900= 12,500 
12,500  -  6,200  at 800=  6,300
6,300 - 4,100 at 700      =  2,200  at 600
<em><u /></em>
<em><u>Ending Inventory </u></em>
3,000 at $600 = $ 1,800,000
COGS:
15,500 x 900 + 6,200 x 800 + 4,100 x 700 + 2,200 x 600 = 23,100,000