Answer:
3
Explanation:
Mary took 3 more than twice as many flights this year as she did last year. Mary took 9 flights this year. How many flights did she take last year?
y = last year
9 = 2y + 3
subtract 3 from both sides:
9 - 3 = 2y + 3 -3
9 - 3 = 2y
6 = 2y
divide both sides by 2:
6/2 = 2y/2
y = 3