Describe the set of points in space whose coordinates satisfy the given combination of equations and inequalities.
a. 1< _x^2 + y^2 + z^2< _4
b. x^2 + y^2 + z^< _4, x> _0

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?