Answer:
Discounted payback period shall be as follows:
a. 1 year 7.36 months
b. 2 years 3.27 months
c. 3 years 2.9 months
Explanation:
a. Payback period in case of cash outflow = $5,700
For calculating the pay back period we shall firstly discount the cash flows to present value @14 %.
Year         Cash Flow         PV Factor           PV of Cash Flow       Cumulative
                                                                                                             Cash Flow
0                 -  $5,700            1                             - $5,700                    -5,700
1                     $4,400         0.877                         $3,858.8                -$1,841.2
2                    $3,900         0.770                         $3,003                    $1,161.8
Since the cumulative cash flows are positive in 2nd year payback period = 
1 +  = 1 year and 7.36 months
 = 1 year and 7.36 months
b. Payback period in case of cash outflow = $7,800
For calculating the pay back period we shall firstly discount the cash flows to present value @14 %.
Year         Cash Flow         PV Factor           PV of Cash Flow       Cumulative
                                                                                                             Cash Flow
0                 -  $7,800            1                             - $7,800                    -7,800
1                     $4,400         0.877                         $3,858.8                -$3,941.2
2                    $3,900         0.770                         $3,003                    -$938.2
3                    $5,100          0.675                         $3,442.5                  $2,504.3
Since the cumulative cash flows are positive in 3rd year payback period = 
2 +  = 2 years and 3.27 months
 = 2 years and 3.27 months
b. Payback period in case of cash outflow = $10,800
For calculating the pay back period we shall firstly discount the cash flows to present value @14 %.
Year         Cash Flow         PV Factor           PV of Cash Flow       Cumulative
                                                                                                             Cash Flow
0               -  $10,800            1                          - $10,800                   -$10,800
1                   $4,400         0.877                         $3,858.8                 -$6,941.2
2                  $3,900         0.770                         $3,003                    -$3,938.2
3                  $5,100          0.675                         $3,442.5                   -$495.7
4                  $4,300          0.592                        $2,545.6                   $2,049.9
 Since the cumulative cash flows are positive in 4th year payback period = 
3 +  = 3 years and 2.9 months
 = 3 years and 2.9 months
Final Answer
Discounted payback period shall be as follows:
a. 1 year 7.36 months
b. 2 years 3.27 months
c. 3 years 2.9 months