\(\left|x-\dfrac{2}{5}\right|=1\Rightarrow\left[{}\begin{matrix}x-\dfrac{2}{5}=1\\\dfrac{2}{5}-x=1\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=\dfrac{7}{5}\\x=-\dfrac{3}{5}\end{matrix}\right.\)
Với \(x=\dfrac{7}{5};y=3\Rightarrow B=\left|\dfrac{7}{5}-\dfrac{3}{8}\right|+\dfrac{1}{3}\cdot3=\dfrac{41}{40}+1=\dfrac{81}{40}\)
Với \(x=-\dfrac{3}{5};y=3\Rightarrow B=\left|-\dfrac{3}{5}-\dfrac{3}{8}\right|+\dfrac{1}{3}\cdot3=\dfrac{39}{40}+1=\dfrac{79}{40}\)