Well we know that the vial contains 60 ounces of medicine, and that 1 dose = 3 ounces.
To find the total number of doses the vial contains, we have to divide the total number of ounces of medicine by the number of ounces 1 dose has.
60 ÷ 3 = 20
So there are 20 doses in 1 60-ounce vial of medicine.
Hope I helped!