Statement (1) only tells us that the total revenue is $270.

Here are some scenarios consistent with the intro and statement (1):

- the store sold 1 sweater that it purchased for $240 and sold for $270.
- the store sold 2 sweaters that it purchased for $105 each and sold for $135 each.
- the store sold 3 sweaters that it purchased for $60 each and sold for $90 each.

As soon as there's more than 1 possible answer (i.e. we didn't need the 3rd example to move on with our lives), we know that statement (1) is insufficient.

Statement (2) tells us that the sale price of each sweater is 1.5 times the cost. Since we know that SP - cost = 30, that's enough information to calculate the sale price (2 equations, 2 unknowns). However, since we don't know how much money they either spent or brought in from sales, we can't calculate the # of sweaters.

If we combine the statements, we know from (1) that SP * # of sweaters = 270 and we know from (2) what the SP is. Therefore, combining the statements will give us enough information to calculate the # of sweaters sold.

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FYI - your error was in your original equation. SP(x) - C(x) doesn't equal total revenue, it equals total profit. Total revenue is simply SP(x).

Revenue = SP * quantity. You are computing it incorrectly.