max 4 x1 + 6 x2 + 7 x3 + 8 x4
s.t.
x1 + x2 + x3 + x4 = 950
x4 > 400
2 x1 + 3 x2 + 4 x3 + 7 x4 < 4600
3 x1 + 4 x2 + 5 x3 + 6 x4 < 500