This question asks "For what amount for the total weekly sales would both salespeople earn the same compensation"
It is not asking for the amount of compensation, rather the total weekly sales. But you do need to make sure what their compensations are the same.
When I first worked this question, I knew right away it was a question where I could manipulate the possible answers to determine the correct answer. Afterward, I reduced it to an equation. I'll show what I did first:
1. Assuming $4,000 is the correct answer, salesperson A's compensation is 6% above $1,000 plus $360. $4,000 is $3,000 above $1,000. So, I took ($3,000 x 6) /100 + $360 = $540. With salesperson B, there is no given condition that states that the percentage is factored only if total sales is above $1,000. So, with salesperson B, you just calculate ($4000 x 8) / 100 = $320 which is not the same as person A's compensation; thus eliminating choice (E)
2. For answer choice (D), $4,500 is $3,500 above $1,000; (3500 x 6) / 100 + 360 = 570 compensation for Sales A. For Sales B, (4500 x 8) / 100 = 360, not the same comp as SP A.
3. I got lucky, because I did not have to eliminate all answers seeing as the right answer was in the middle - (C). (14000 x 6) / 100 + 360 = $1200. (15000 X 8) /100 = $1200, which is the same compensation as SP A. Therefore, the correct answer is (C) $15,000 total sales for both person A and B would give same compensation.
However, on the real GMAT test, this may take too long for some, and a simple equation is needed to account for time.
Let X = total sales
1. 360 + 0.06 (x-1000) = 0.08x
2. 360 -60 = 0.08x
3. 300/0.02 = x
4. 15000 =x
Hope this helps