Can you help me to figure out the answer?

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In southern California a photovoltaic (PV) system for a certain home costs $30,800 for parts and installation. This 6.1 kW system requires 300 ft? of rooftop space and has an estimated life of 22 years. a. If this PV system saves $220 each month in electricity expenses, what is the simple payback period in months? b. If the market value of the PV system is negligible, what is the system's IRR? a. The simple payback period for the PV system is months. (Round to the nearest whole number.) b. The IRR of the PV system is % per month. (Round to one decimal place.)