F(x) = -2x1 + x2 + 2x3 + 1,5x4 + x5 min
x1 - 2x2 + 2x3 - x4 = 12
2x2 +x3 +x4 + x5 =10
2,5x1 + x2 -x3 =< 15
xj >= 0, (j= 1,5)
