Mary can paint a house by herself in 12 hours. john can paint a house by himself in 16 hours. how long would it take them to paint the house if they worked together?

Sarah took the advertising department from her company on a round trip to meet with a potential client. including sarah a total of 11 people took the trip. she was able to purchase coach tickets for $280 and first class tickets for $1280. she used her total budget for airfare for the trip, which was $6080. how many first class tickets did she buy? how many coach tickets did she buy?