Data Sufficiency

Dear Gurus,
Please help me to understand the question and especially answer .This is from Veritas Prep.
Will raise my doubt underneath where explanation is given.
Question:Last Friday, a certain shop sold 3/4 of the sweaters in its inventory. Each sweater
sold for $20. What was the total revenue last Friday from the sale of these
sweaters?
(1) When the shop opened last Friday, there were 160 sweaters in its inventory.
(2) All but 40 of the sweaters in the shop's inventory were sold last Friday.
(A) Statement (1) ALONE is sufficient, but statement (2) alone is not
sufficient to answer the question asked
(B) Statement (2) ALONE is sufficient, but statement (1) alone is not
sufficient to answer the question asked
(C) BOTH statements (1) and (2) TOGETHER are sufficient to answer the
question asked, but NEITHER statement ALONE is sufficient
(D) EACH statement ALONE is sufficient to answer the question asked
(E) Statements (1) and (2) TOGETHER are NOT sufficient to answer the
question asked, and additional data are needed
OA D
---Explanation:
If we know that each sweater costs 20 USD ,we just need to know how many sweaters were sold to find the revenue(Revenue=cost/unit X no of units sold).
Sentence 1:tells us the no we sold 3/4 of 160=120,meaning we sold 120 sweaters and is thus sufficient.
2)will tell us that 1/4 we didn't sell equals 40,which we subtract from 160 to get 120.So they are both sufficient.

I have a issue over here.When we are analyzing the statements in DS we have to ideally evaluate individual!Right?
Then why here its being considered that for statement 2 we actually subtract from 160.How do we get that information from statement 2 alne.The total number is being in statement 1 only.
IMO it should be A.
Please give your comments on this.
Regards,
Dhiren