When using the fifo or lifo method to compute cost of goods sold and ending inventory, how do you determine what goes in the ending inventory column and what goes into the cogs column.
Example:
Opening Inv. 9,000 units@ $16
Purchase 4/16: 27,000 units @ $18
Purchase 7/28: 30,000 units @ $23

How would that be split to get the EI and the COGS?

First, you have to tell me how many units you sold.

Let's assume you sold 31,000 units.

FIFO:
First in-First out.
So, COGS would be the first 31,000 units.

That is,
9,000 x 16  Opening Inv. 9,000 units@ $16
22,000 x 18  purchase 4/16: 27,000 units @ $18

Ending inventory would be the remaining 35,000 units
5,000 x 18  purchase 4/16: 27,000 units @ $18
30,000 x 23 purchase 7/28: 30,000 units @ $23


LIFO
Last-in last-out.
You expense your latest products first.
So, COGS would be 31,000, but they would consist of:

30,000 x 23 purchase 7/28: 30,000 units @ $23
1,000 x 18  purchase 4/16: 27,000 units @ $18

And your ending inventory would be 35,000 units, but their value would be:
26,000 x 18  purchase 4/16: 27,000 units @ $18
9,000 x 16 Opening Inv. 9,000 units@ $16