1 liter is equal to 1000 milliliters, so we can multiply 200 liters by 1000 to get 200000 milliliters, which should be your answer. In general, the "milli-" prefix denotes a factor of one thousand times smaller, so 1 meter is equal to 1000 millimeters, 1 second is equal to 1000 milliseconds, and so on.
