I need to know how to solve number 14, I don't just need the answer.

Aschool allots ? 1500 to spend on a trip to the theatre. theatre tickets have a regular cost of ? 55 each and are on offer for 1 5 off. a train ticket for the day will cost ? 12 each. if 2 teachers and the maximum number of students attend, how much money will the school have left over?

Find the measure of angle a in the following triangle

What are the triple angle formulas? is it related to double angle identities?