Bob's books ships 300-450 books a month. Some are shipped from store A and some are shipped from store B, but at least one third must be shipped from each warehouse. It costs 37 cents from store A and 55 cents from store B. Minimize the cost.

So x=number from store A and y=number from store B.

Now would the constraints be:

x+y>=300, x+y<=450

x>=100, y>=100, x<=300, x<=300

or would they be

x+y>=300, x+y<=450

x>=(y/3), x<=2y/3, y>=(x/3), y<=(2x/3)