In this above question,

we add the integral part and fractional part separately.

$$\begin{gathered} = ?=3+\frac{3}{4}+4+\frac{2}{5}-\left(3+\frac{1}{8}\right) \\ =?=(3+4-3)+\left(\frac{3}{4}+\frac{2}{5}-\frac{1}{8}\right) \\ =?=4+\left(\frac{30+16-5}{40}\right)=\frac{160+41}{40} \\ =5\frac{1}{40} \end{gathered}$$

Hence, Option B is correct.