Math Khan Academy 8th grade

Evaluate the expression for the given value of the variable 7a - 4a for a =8

Which representation has a constant of variation of -2.5

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?