Linear Programming Problem

A box manufacturing plant makes two types of boxes, each of which requires time on the saw for cutting, then time on the assembly and later for finishing. Suppose Model A requires 1 hour cutting, 2 hours of assembly and 1 hour of finishing. Model B requires 1 hour of cutting, 1 hour of assembly and 3 hours of finishing. There are 40 man hours available for cutting per week, 60 man hours for assembly and 90 man hours for finishing. Suppose each model A box sold brings in $20 profit and each model B box sold brings in $25 profit. Determine the number of each box that should be produced to maximize the profit.