John thunderhawk is making furniture. he finds that to design a particular cabinet and set up his shop to produce it costs $1,800. then the labor and supplies to build each one are $400. so his cost, y, for x items is represented by y=1,800 + 400x. he can sell the cabinets for $600. so his revenue, y, is represented by y=600x. the solution to this system of equations is his break-even point, the point beyond which he starts making a profit. how many cabinets must he sell to break-even?