Journal correction - Closing Inventory NEED HELP PLEASE!!

There are 2 questions that I just do not understand.
My teacher says when calculating closing Inventory you need to do "Cost of Inventory" LESS (selling price LESS costs incurred to make it sell able) but the text book says Inventories are to be valued at "the lower of cost and net realisable value"
Could someone explain this to me.
First One:

Second One:
No entries have been made for closing inventory as at 31 December 20X8, It has been valued at a selling price of £227,184. The sales price has had 20% added onto its original cost
My teacher says when calculating closing Inventory you need to do "Cost of Inventory" LESS (selling price LESS costs incurred to make it sell able) but the text book says Inventories are to be valued at "the lower of cost and net realisable value"
Could someone explain this to me.
First One:

Second One:
No entries have been made for closing inventory as at 31 December 20X8, It has been valued at a selling price of £227,184. The sales price has had 20% added onto its original cost
0
Comments
Net realisable value is simply the selling price less the cost of making the goods sellable. If that value is less than the cost of the goods originally, then that would be value of the inventory. I think this is what your teacher is trying to say.
For d) you have a transposition error and need to correct it depending on space you either reverse the incorrect entry and enter the correct one or just the correction amount of £630.
ACCA in progress
F4- Passed Aug 2020
F5- Planned for Dec 2020
F6- Passed Sep 2020
F7
F8
F9