MCB Ltd$.$ uses a perpetual inventory system and reports the following transactions for the month of January:

January $1$ Beginning Inventory, $30,000$ units purchased at $$20$ per unit.

January $5,$ Purchased with cash $30,000$ units merchandise at $$24$ per unit.

January $10$ Sold with cash $45,000$ units merchandise at $$24$ per unit.

January $15$ Purchased on account $15,000$ units merchandise at $$30$ per unit.

January $20$ Purchased with cash $30,000$ units merchandise at $$34$ per unit.

January $25$ Sold on account $40,000$ units merchandise at $$40$ per unit.

Required:

$(1)$ Under the FIFO Cost$-$flow method, $(2)$ Under the LIFO Cost$-$flow method, and $(3)$ Under the Weighted Average Cost$-$flow method;

a$.$ Journalize the transactions and prepare the ledger accounts $($T$-$accounts$)$

b$.$ Calculate Gross Profit

c$.$ Calculate Gross Profit Margin

d$.$ Calculate the Cost of Ending Inventory