35 necklaces multiplied by 4 weeks is 140. Multiply 140 by 15, representing the amount of money each necklace costs and you get 2,100. That is the total amount sold, but because the 6 costumers brought their necklaces back, you have to take 6 times 15 to see how much the total returned necklaces cost. That would be $210, so you take $2,100 and subtract $210, and your answer is $1,180. That is the final answer.