P&G sells carpet cleaning kits. It sells these kits for $120. The costs of the materials that go into each kit are $45. It costs $5 in labour to assemble a kit. The company has monthly expenses of $1,000 for rent and insurance, $200 for heat and electricity, $500 for advertising in trade journals, and $3,500 for the monthly salary of its owner. How many kits must P&G sell per month to break even?