Answer:
8 years
Step-by-step explanation:
Given: Cost of new machine= $500000.
 Annual cash inflow= $100000.
 Annual cash outflow= $37500.
First, we will calculate annual payback or cash inflow.
Annual payback= 

∴Annual payback= 

Now computing cash payback period.
Cash payback period= 

Cash payback period= 

∴ Cash payback period is 8 years.
When payback period is short then investment is more attractive.