First,
Let x be the Quartz and let y be the Pacer.
We can write:
x+y≤1200 ( maximum production capacity of 1200 cars per week)
We also know that:
0≤x≤600
0≤y≤800
And, the profit is given by the expression: 500x+800y
At a point, we got that : x=0 and y=800. So, if we replace this:
Profit=500x+800y ⇒ 500(0) + 800(800)= 640000
When x=600(max), y=0:
profit = 500(600) + 0 = 300000
Using (x,y) = (600,600):
Profit = 500(600)+800(600)= 780000
And, if we make x=400 and y=800:
Profit =500(400)+800(800) = 840000. This is the maximum profit, and it occurs when Quartz = 400 and Pacers = 800.