As we know that, NPV = sum of discounted cash flows - initial investment
Initial investment = 438,000 + 29,000 = $467,000
Cash flows:
Each year, $129,000 are saved by the system so it is positive cash flow
Also, each year tax is also saved on depreciation expense. it is = 438,000 * 0.35/4 = $38,325
Net yearly cash flow = 129,000 + 38,325 = $167,325
Additional cash flow from the scrapped system at the end of fourth year = $69,000
So, NPV = 167,325/1.09 + 167,325/(1.09)^2 + 167,325/(1.09)^3 + (167,325+69,000)/(1.09)^4
= 153,509 + 140,834 + 129,206 + 167,419
= $590,968