A company produces hammers and screwdrivers using three resources (metal, rubber, manufacturing time). Hammers require 4 units of metal, 2 units of rubber and 1.5 units of manufacturing time. They earn a profit of $3. Screwdrivers require 2 units of metal, 2 units of rubber and 1 unit of manufacturing time. They earn a profit of $2. There is a maximum of 50 units of metal, 40 units of rubber, and 60 units of manufacturing time. Write the linear program (define the variables, write the objective function, and all constraints).