For a certain proposed structural system, x1 and x2 are nonzero quantities that represent the extents of two design inputs A and B, respectively. It is desired that the sum of 2 units of A and 4 units of B must not exceed 21 units; also, the sum of 5 units of A and 3 units of B must not exceed 18. Maximize the overall structural performance of the system, denoted as Z, where C is the sum of 3 units of A and 2 units of B. (a) On a graph sheet, clearly show the feasible region for the constraint set and label all vertices of the feasible region. Using an appropriate software platform, determine the optimal solution.