A construction firm specializes in building and selling single-family homes. The firm offers two basic types of houses: model A and model B. Model A houses require 4000 labor hours, 2 tones of stone, and 2000 board feet of lumber. Model B houses require 10000 labor hours, 3 tones of stone, and 2000 board feet of lumber. Due to long lead times for ordering supplies and the scarcity of skilled and semi-skilled workers in the area, the firm will be forced to rely on its present resources for the upcoming building season. It has 400000 hours of labor, 150 tones of stone, and 200000 board feet of lumber. What mix of model A and B houses should the firm construct