Foremost Corporation manufactures boxes. The estimated numbers of boxes sold for the first three months of the current year are as follows:

Month

January

February

March

Sales

$3,000$

$4,200$

$3,900$

Finished goods inventory at the end of December was $900$ units. Ending finished goods inventory is equal to $20\%$ of the next month's sales. Foremost Corporation expects to sell the boxes for $$5$ each. April sales is projected at $4,500$ boxes.

What is the expected sales revenue for March?

a$.$ $$15,000$

b$.$ $$19,500$

c$.$ $$4,500$

d$.$ $$21,000$