Question 35573
Are you sure you have the data correct?
Inequalities based on your posted data give:
2.5a+3b<=4000
2a+b<=2500
0.5a+1.25b<=1500
Plotting these you get a triangle 
with two vertices belog the "a" axis indicating
negative production of model "b".
Only one axis has a meaningful interpretation,
i.e. (1000,0)
Indicating production of 1000 model "a" and no "b"
That would give a profit of 1000(50) = $50,000 

Does this sound reasonable?
Cheers,
stan H.