Let the merchant stock x desktop models and y portable models. Therefore,
x ≥ 0 and y ≥ 0
The cost of a desktop model is Rs 25000 and of a portable model is Rs 4000. However,
the merchant can invest a maximum of Rs 70 lakhs.

The monthly demand of computers will not exceed 250 units. The
x+y ≤ 250
The profit on a desktop model is Rs 4500 and the profit on a portable model is Rs 5000.
Total profit, Z = 4500x + 5000y
Thus, the mathematical formulation of the given problem is

The feasible region determined by the system of constraints is as follows.

The corner points are A (250, 0), B (200, 50), and C (0, 175).
The values of Z at these corner points are as follows.

The maximum value of Z is 1150000 at (200, 50).
Thus, the merchant should stock 200 desktop models and 50 portable models to get the
maximum profit of Rs 1150000.