The LP relationships that follow were formulated by Jeffrey Rummel at the Connecticut Chemical Company. Which ones

Question:

The LP relationships that follow were formulated by Jeffrey Rummel at the Connecticut Chemical Company. Which ones are invalid for use in a linear programming problem, and why?
Minimize = 6X1 + ½X1 X2 + 5X3
Subject to: 4X1X2 + 2X3 ≤ 70
7.9X1 – 4X2 ≥ 15.6
3X1 + 3X2 + 3X3 ≥ 21
19X2 – 1/3 X3 = 17
– X1 – X2 + 4X3 = 5
4X1 + 2X2 + 3√X3 ≤ 80