Answer:
Net present value = -$22,531
Explanation:
As per the data given in the question,
Computation of NPV project
Particulars Period            Pv factor at 14%    Amount            Present value
Cash inflows:
Annual saving in costs 1-7 4.288305           $112,000              $480,290
Salvage value 7                  0.399637           $52,000              $20,781
Recovery of working capital 7 0.399637     $6,000                $2,398
Present value of cash inflows                                                $503,469
Less: Cash outflows
Cost of Machine     0                 1                  $520,000           $520,000
Working capital       0                1                  $6,000                $6,000
Net present value                                                                     -$22,531
Working Note 
The present value of cash inflows is 
$480,290+ $20,781+$2,398 = $503,469
And, the net present value is 
= $503,469- $520,000-$6,000 
= -$22,531