Explanation:
your teacher gave you the solution to the real problem of this question : how many cups are in 1 gallon. 16 cups.
and if you remember that a year has 365 days, then the rest is rant simple and straight forward :
8 cups per day
so
365 × 8 = 2920 cups per year.
2920 cups = 2920/16 = 182.5 gallons
therefore, she drinks 182.5 gallons of water per year.