A used book store started selling CDs and videos. In the first week, the bookstore started selling 40 CDs and videos. They charged $4 per CD and $6 per video. The total sales was $180. Which system of equations corresponds to this situation?

Two spray paint machines are used to paint different portions of a large wall. the first machine (nicknamed "paint pro") is used for two hours. the second machine (nicknamed "goldilocks") is used for an hour and a half. when they are working at the same time, they can paint 55 square feet per minute. together they painted 5850 square feet of wall. how many square feet of wall per minute can each machine paint? e used to paint different portions of a large wall. the first machine (nicknamed "paint pro") is used for two hours. the second machine (nicknamed "goldilocks") is used for an hour and a half. when they are working at the same time, they can paint 55 square feet per minute. together they painted 5850 square feet of wall. how many square feet of wall per minute can each machine paint?