Well your smallest common measure here is milliliters, and you want to know number of glasses in Ml also, so you can begin by converting all quantities to milliliters.

There are 1000 milliliters in 1 liter.

3 liters = 3000 milliliters soda

add: 1893 Ml cranberry juice

(so without the vodka ...LOL) you have 4893 milliliters of punch total.

Now divide 4893 by 250 to find out how many 250 Ml glasses of punch can be had: 4893/250= 19.572 glasses. Rounded (up) to nearest tenth is 19.6 glasses (just a little over 19 and a half glasses)

There are 1000 milliliters in 1 liter.

3 liters = 3000 milliliters soda

add: 1893 Ml cranberry juice

(so without the vodka ...LOL) you have 4893 milliliters of punch total.

Now divide 4893 by 250 to find out how many 250 Ml glasses of punch can be had: 4893/250= 19.572 glasses. Rounded (up) to nearest tenth is 19.6 glasses (just a little over 19 and a half glasses)