Arestaurant can hold at most 40 people

Given the two similar triangles, how do i find the missing length? if a=4, b=5, and b'=7.5 find a'

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?

Solve for the equation. 4x - 13 = 2x + 9