So I'm Assuming your question was a bottle contains 3.5 liters of water, A second bottle contains 3,750 milliliters of water, How many more milliliters of water are in the larger bottle that in the smaller bottle?
so first you have to change 3.5 liters to milliliters the you subtract
1 liter = 1000 milliliters
3.5 liters = 1500 milliliters
3,750 milliliters (large bottle)
-1,500 milliliters
---------
2,250 milliliters That's your answer