So the question tells to express the expression in your problem where N0 is N-naught and the symbol represent the lower case Greek letter lambda. So the best answer or expression would be that the lambda is the wavelength of the expression. I hope you are satisfied with my answer
The answer is 16 cm (or 0.16 m).
The scale is the ratio of the model to the real thing.
So, in the scale 1:50, the model is 1, while the real thing is 50.
Now, just make a proportion:
the model : the real thing = the model dimension : the real thing dimension
1 : 50 = x : 8m
From here:
x = 8m * 1 / 50 = 0.16 m = 0.16 * 100 cm = 16 cm.