How To Calculate A 2m To The Scale 1-4?

Please show your work, it looks like you have changed the numbers around.

The work *is* shown. A scale factor is generally a ratio between the model size and the "real" size. In this case, I computed that the 1/4 scale model would use 50 cm to model a real-world distance of 2 m. The question is non-specific as to whether the given distance is the model distance or the real-world distance, so I made a choice.
If you want the 2 m to represent the model distance, then, as you say, the numbers are "changed around." The real-world distance in that case is (2 m)/(1/4) = 8m.