Okay so your problem can be answered like this: So you have 1.2 liters of water in the bottle, but he drank 200 milliliters of that water. In order to find how much he has left, you would have to convert the amount of liters he had in his bottle (1.2) to milliliters. Once you find that, subtract the amount he drank (200mL) from the amount he had in the bottle (it should be in mL). After all that, your problem will be solved and if it says to put the answer as liters, just convert the difference back into liters. I hope this helps you!