Consider an economy that produces only phones. In the year 2019, 500 workers produced 100 phones, which were all sold at a price of $100. In the year 2020, 600 workers produced 120 phones, which were all sold at a price of $120. Between 2020 and 2019, what was the percentage increase of average labour productivity (use 2019 as the base year)?

0%

-20%

44%

20%