Minimise
\[
Z = \sum_{i=1}^{n} \sum_{j=1}^{m} c_{ij} x_{ij}
\]
Subject to:
\[
\sum_{i=1}^{n} x_{ij} = b_j, \quad j = 1, 2, \dots, m
\]
\[
\sum_{j=1}^{m} x_{ij} = b_i, \quad i = 1, 2, \dots, n
\]
This is a linear programming problem (LPP) with number of constraints: