Answer:
Payback period is 6.5625 years
Step-by-step explanation:
All amounts are in $
Item outflow inflow balance
Year 0 387,000 0 (387,000)
Year 1 0 64,000 (323,000) 
Year 2 0 64,000 (259,000) 
Year 3 0 64,000 (195,000) 
Year 4 0 64,000 (131,000) 
Year 5 0 64,000 (67,000) 
Year 6 0 64,000 (3,000)  
The remaining $3000 will flow in
= (3000/64000) × 12
= 0.5625
Payback period is 6.5625 years