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?