Cut and Stitch

Cut and Stitch (CS) make two types of suits using skilled tailors (labour) and a delicate and
unique fabric (material). Both the tailors and the fabric are in short supply and so the
accountant at CS has correctly produced a linear programming model to help decide the
optimal production mix.
The model is as follows:
Variables:
Let W = the number of work suits produced
Let L = the number of lounge suits produced
Constraints
Tailors’ time: 7W + 5L < 3,500 (hours) – this is line T on the diagram
Fabric: 2W + 2L < 1,200 (metres) – this is line F on the diagram
Production of work suits: W < 400 – this is line P on the diagram
Objective is to maximise contribution subject to:
C = 48W + 40L
On the diagram provided the accountant has correctly identified OABCD as the feasible
region and point B as the optimal point.

Calculate the new optimum production plan if maximum demand for W falls to
200 units. ?

They have taken Line F to solve the equation stating that Line F and w=200 intersect at the optimal point. I didn’t understand.