Study the given bar graph and answer the question that follows.
A tea plantation company produces three varieties of tea—black tea, green tea and herbal tea. The production of three varieties (in million tonnes) over a period of six years from 2014 to 2019, has been shown in the bar graph here. The X-axis represents the years and the Y-axis displays the production of the three varieties in million tonnes.

The average production of black tea in 2014, 2015 and 2018 is how much more or less(in million tonnes) than the average production of green tea in 2016, 2017 and 2019?