"the quotient of a number and 2, increased by 9 is -15" (im working on translating expressions and im very confused)

Abacteria population is tripling every hour. by what factor does the population change in 1/2 hour? select all that apply

A50% increase followed by 33 1/2% decrease

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?