Jake plans to make and sell wooden birdhouses. He plans to sell each birdhouse for $50, his income can be found using the equation I(x) = 50x, where x is the number of birdhouses he sells. It costs him $10 in materials for each birdhouse, so his expenses can be found using the equation E(x) = 10x. Use function operations to find an equation for his profit, P(x), and find his profit if he sells 20 birdhouses.