please help me with this review question.

Problem 4 (20) The process for producing integrated circuit for computer mother board has a first cost of $500,000 (initial investment at year 0) with annual cost $80,000 and revenue of $270,000 per year starting 5 years from now. In year 7, $25000 was given to the company by Environmental Protection Agency as credit for its environmental compliance. What is the payback period at a) 0% b) 11% Given the two guesses for Payback Period to be between 5 yrs and 6 yrs at 11 % besides 4 years of no expenses and no revenue Problem 4 (20) The process for producing integrated circuit for computer mother board has a first cost of $500,000 (initial investment at year 0) with annual cost $80,000 and revenue of $270,000 per year starting 5 years from now. In year 7, $25000 was given to the company by Environmental Protection Agency as credit for its environmental compliance. What is the payback period at a) 0% b) 11% Given the two guesses for Payback Period to be between 5 yrs and 6 yrs at 11 % besides 4 years of no expenses and no revenue