The remainder function can be defined for all real numbers x and y with y \neq 0 by
\operatorname{rem}(x, y)=x-y\left\lfloor\dfrac{x}{y}\right\rfloor
where \left\lfloor\dfrac{x}{y}\right\rfloor denotes the greatest integer less than or equal to \dfrac{x}{y}. What is the value of \operatorname{rem}\left(\dfrac{3}{8},-\dfrac{2}{5}\right) ?
Answer Choices
A. -\dfrac{3}{8}
B. -\dfrac{1}{40}
C. 0
D. \dfrac{3}{8}
E. \dfrac{31}{40}