You know that a "2% m/m" sucrose solution must contain "2 g" of sucrose for every "100 g", so right from the start you can say that the total mass of the solution will be equal to "100 g".
Now, you're making this solution by adding "2 g" of sucrose to water, so use the total mass of the solution to figure out exactly how much water you need
"2 g sucrose"color(white)(.) + xcolor(white)(.)"g water" = "100 g solution"
You will end up with
x = "100 g" - "2 g"
x = "98 g"
You got to the answer by subtracting your value from a constant, i.e. from "100 g" of solution, so the answer must not have any decimal places because of the fact that "2 g" of sucrose doesn't have any decimal places.
Therefore, you can say that in order to make a "2% m/m" sucrose solution, you need to add "2 g" of sucrose to "98 g" of water.