let the number be 'x'

Given that the difference between the number is $\frac{3}{5}$ of the number is 40

 $$\begin{gathered} = x-\frac{3}{5x}=40 \\ = \frac{5x+(-3x)}{5}=40 \\ = \frac{2x}{5}=40 [multiply both sides of the equation by \frac{5}{2}] \\ = \frac{5}{2}\times \frac{2x}{5}=\frac{5}{2}\times 40 \\ = \frac{1}{2}\times 2x=\frac{5}{2}\times 40 \\ = x=\frac{5}{2}\times 40 \\ =x=100 \end{gathered}$$

Hence, Option D is correct.