Assume the following data for Year $6$:

January $1$Beginning inventory is $10$ units at $$7$ each.

March $18$Purchase $15$ units at $$9$ each.

June $10$Purchase $20$ units at $$10$ each.

October $30$Purchase $12$ units at $$11$ each.

December $31$Physical count reveals $15$ units in ending inventory.

Assume a perpetual inventory system and all sales occurred prior to October $30.$ Under the FIFO method, cost of goods sold on the income statement would be:

a$.$ $$375.$

b$.$ $$537.$

c$.$ $$162.$

d$.$ $$420.$

Can someone please explain step by step how to solve this? The answer according to the practice exam answer key is $$375.$