Answer:
75%
Step-by-step explanation:
Given that,
No. of workstations used = 10
Target output for an 8 hour workday = 120 bags
Sum of the task times = 30 minutes/bag
Cycle time = 4 minutes/bag
Assembly-line efficiency: 
= Sum of the task times ÷ (Number of work stations × Cycle time) 
 = 30 ÷ (10 × 4 ) 
 = 30 ÷ 40 
 = 0.75 
 = 75%
Therefore, The assembly-line efficiency is 75%.