If you are really going to mow 4 acres regularly, choose the commercial mower. They are made for mowing lots of land and for many more hours of usage. They cost more but last a very very long time with regularly scheduled maintenance of engine and eq...
check your local classifieds; check with a dealer who takes trade-ins. Check with an on-line site such as Craigslist or the auction sites for completed sales.
2) Increasing returns it cost $60 per mower when making either 300 or 400 mowers, but only cost $48 per mower when making 500. Assuming she charges the same price for mowers, her returns are greater (increase) when she produces 500 compared to 300 or...