Manu plc was established on $1$ January $202$ with a share capital of $20,000$ in cash. The following information is available:

On $5$ January $20$X$2,$ Manu plc bought $100$ units of product, for a cost of $50$ per unit.

On $10$ January $20$X$2,$ Manu plc sold $60$ units for a price of $90$ per unit.

On $25$ January $202,$ Manu plc sold $20$ more units for a price of $100$ per unit.

All the transactions above were settled in cash.

The realisable value per unit of product was:

$65$ on $5$ January $202$

$90$ on $10$ January $202$

$100$ on $25$ January $202$

$110$ on $31$ January $202$

Which of the following statements about realisable value accounting $($RVA$)$ is correct?

a$.$ Cost of sales for the month of January is $7,400.$

b$.$ A capital adjustment of $1,200$ is recognised as a liability item in the statement of financial position for the month of January.

c$.$ Holding gain on inventory is $1,200.$

d$.$ A capital adjustment of $1,200$ is recognised in the equity section in the statement of financial position for the month of January.