Answer:
The efficiency of this line is 0.85 = 85%.
Step-by-step explanation:
Efficiency:
The efficiency is given by the following formula:

In which
is the total task time,
is the largest assigned cycle time and n is the number of workstations.
5 workstations
This means that 
The sum of the 21 task times is 85 minutes.
This means that 
The largest assigned cycle time is 20 minutes.
This means that 
What is the efficiency of this line?

The efficiency of this line is 0.85 = 85%.