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Wouldn't part b of this question be correct? It asks for the wavelengths that correspond to the upper and lower. Isn't Violet (with a wavelength of 400 nm) on the upper end?
So the correct answer is $\displaystyle \lambda = 400nm$ for the one on the left and $\displaystyle \lambda = 700nm$ for the one on the right since you are considering the range. In wavelength terms Red is in the upper end, in frequency and therefore energy terms $\displaystyle E = hf$ violate is in the upper end.