Find the area of a compound shape

Can you please explain

7x+8y=-18, 4x-9y=-3 solve the system of equations

Can someone me and do the problem plz so i can understand it more better

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?