What is the total mass of a solution prepared by dissolving 4.00 of in 1.00 of water?
4.00 what in 1.00 what of water?
If that is 4.00 g in 1.00 L of water the answer is 4.00 + 1000 = 1004 grams.
BUT if it is 4.00 g in 1.00 mL of water, the answer is 4.00 + 1.00 = 5.00 grams.