You can pay $91 per month, starting next month, for the next 5 years to have a lawn mowing service. Alternatively, you can purchase a riding lawn mower and pay $506 today and mow your own lawn for 5 years, starting next month. If you decide to mow your own lawn, how much do you save in PV terms if your investments earn 3.31% APR, compounded monthly? Note: If you would lose money, make your answer with a negative sign (e.g., - 3458)