Draw the Network for This Assignment Problem

Essay

Draw the network for this assignment problem.
Min
10x_1A + 12x_1B + 15x_1C + 25x_1D + 11x_2A + 14x_2B + 19x_2C + 32x_2D
+ 18x_3A + 21x_3B + 23x_3C + 29x_3D + 15x_4A + 20x_4B + 26x_4C + 28x_4D
s.t.
x_1A + x_1B + x_1C + x_1D = 1
x_2A + x_2B + x_2C + x_2D = 1
x_3A + x_3B + x_3C + x_3D = 1
x_4A + x_4B + x_4C + x_4D = 1
x_1A + x_2A + x_3A + x_4A = 1
x_1B + x _2B + x_3B + x_4B = 1
x_1C + x _2C + x_3C + x_4C = 1
x_1D + x_2D + x_3D + x_4D = 1