Please show formulas not just excel

7. Case 3 (30 points) Frank is considering the purchase of a $20,000 solar electric system to reduce the amount o electricity he purchases from the grid. The system has an area of 20 m2. The average solar flux at Frank's house is 220 W m2 (averaged over 24-hours and over an entire year). Frank pays $0.11 per kWh for electricity from the grid. The solar systern is 15% efficient. Assume that all these numbers are constant for the entire life of the system (i.e., we are modeling this in real terms). Further, assume that Frank will use all the power he produces Assuming Frank will live in his house for 8 years, and using a real MARR of 6% per year compounded yearly, should Frank purchase the system? Assume that when he sells his house the system will have no value and no impact on the price of his home. (15 points) a. Hint: work this problem using a period length of one year, rather than daily or monthly