Set up the general form of the LP model for the following word problem.

A cash grain farmer in Central Iowa has 600 acres of cropland available on which she plans to grow corn and soybeans in the spring of 2011. She has made some budgets, which take into account corn (x) and soybeans (y). The gross margin for corn is $40 per acre and for soybeans is $45 per acre. She has a maximum of 750 hours of tractor time available in the last half of May at the peak planting periods for both crops. It takes 1 hour per acre for field operations for corn (x) and 1.5 hours per acre for soybeans (y). The maximum acreage she can use for corn is 400 acres. Her sole objective is to select a cropping plan that will maximize net returns for this set of conditions in 2011.