Given the Following Process Layout Data for Locating Four Departments

Given the following process layout data for locating four departments (A, B, C, and D) in four areas (1, 2, 3, and 4): $\begin{array}{l}\text { Distances (meters) } \quad\quad\quad\quad\quad\quad \text { Flows (loads per week }\\\begin{array}{rlll}\text { From/To } & 1 & 2 & 3 & 4 \\\hline 1 & - & 50 & 100 & 150 \\2 & & - & 50 & 100 \\3 & & & - & 50 \\4 & & & & -\end{array}\quad\quad\begin{array}{rlll}\text { From/To } & \text { A } & \text { B } & \text { C } & \text { D } \\\hline \text { A } & - & 10 & 40 & 50 \\\text { B } & 30 & - & 10 & 70 \\\text { C } & 60 & 10 & - & 40 \\\text { D } & 30 & 50 & 20 & -\end{array}\end{array}$ What is the total flow between departments B and D?