[SOLVED] Linear programming - modeling a problem

-SOLVED=

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"A factory produces 3 types of trailers made in metal and wood: type I, type II and type III. The factory wants to maximize its profits by producing the right quantity of each type of trailer at each period of production. The factory has a maximum production capacity of 24 days/period for the "metal work" and 60days/period for the "wood work".

I'm having a hard time to model this problem in the form:

(a) variables

(b) economic function to maximize/minimize

(c) constraints

Here's my answer but I don't think the constraints are that simple:

a + 2b + 4c <= 60

1/2a + 2b + c <= 24

a,b,c >= 0

I'll need to solve it using the simplex method.

Thank you

edit: cleaned things up a bit