767

 

 

 

\begin{array}{c}
\Sigma x_{u}=\Sigma y_{u}-\Sigma P R G\left(b_{u}\right)-\sum_{d<m_{j}} \operatorname{PRG}\left(r_{m_{j}}, d\right)+\sum_{d>m_{j}} P R G\left(r_{m_{j}}, d\right)
\end{array}