3/4 of a 6-ounce glass will be drunk by her in one hour.
Step-by-step explanation:
Given time = 2/3 of hour
          = 2/3 (60)    As hour = 60 mins
          = 120/3
          = 40 mins
Given quantity of water = 1/2 of 6-ounce
                    = 3 ounce
So,
  In 40 mins, water intake is 3 ounce
  In 1 min, water intake is 3/40
  In 60 mins, water in take is (3/40)*60 = 4.5 ounce
Quantity of water intake in 60 mins:
    4.5 ounce or 3/4 of 6-ounce glass
I hope it will help you.