Study the table below, which shows the annual volume of municipal solid waste composted (in millions of tonnes, Mt) in a European metropolitan region between 2012 and 2023.
| Year | Composted Waste (million tonnes, Mt) |
|---|---|
| 2012 | 3.2 |
| 2013 | 4.5 |
| 2014 | 6.1 |
| 2015 | 8.4 |
| 2016 | 12.2 |
| 2017 | 15.1 |
| 2018 | 16.8 |
| 2019 | 17.6 |
| 2020 | 18.2 |
| 2021 | 18.8 |
| 2022 | 19.4 |
| 2023 | 20.6 |
Calculate the upper quartile value for this dataset. You must show your working out.