MetaNote: Answer questions $(18)(20)$ based on the following information:

Beginning inv. $0$ units $ $0$

Purchases $($in units$)$:

$6/210$ units @ $$100=$ $ $1,000$

$6/810$ units @ $$120=$ $ $1,200$

Goods available: $20$ units $ $2,200$

Units sold: $15$ units

$18)$ What is Cost of Goods Sold under the FIFO method of inventory?

a$)$ $$1,500$

b$)$ $$1,600$

c$)$ $$1,700$

d$)$ $$1,800$

$19)$ What is Cost of Goods Sold under the LIFO method of inventory?

a$)$ $$1,500$

b$)$ $$1,600$

c$)$ $$1,700$

d$)$ $$1,800$

$20)$ What is the cost of ending inventory under the average cost method of inventory?

a$)$ $$1,000$

b$)$ $ $600$

c$)$ $ $500$

d$)$ $ $550$