Answer:
d. 16.0 minutes
Step-by-step explanation:
 Performance rating = (1+ Allowance factor) 
 Observed time = 160/384 (1-idletime) = 0.41667* (1-0.2) hrs per unit
standard time = Observed time * Performance rating 
 =0.3333 hrs/ unit 
 = 0.3333*(0.8) 
 = 0.26668 hrs per unit
 = 0.26668*60 min/unit
 = 16 min per unit
Therefore, the standard time is 16 min per unit