Some industrial processes release warm water into rivers, affecting the aquatic ecosystem. The table below shows the effect of water temperature on the concentration of dissolved oxygen in a river:
| Water temperature in ∘C^\circ\text{C}∘C | Concentration of dissolved oxygen in mg\text{mg}mg per litre |
|---|---|
| 8 | 11.84 |
| 12 | 10.43 |
| 16 | 9.21 |
| 20 | 8.15 |
Calculate the percentage change in the concentration of dissolved oxygen when the water temperature rises from 12 ∘C12\text{ }^\circ\text{C}12 ∘C to 16 ∘C16\text{ }^\circ\text{C}16 ∘C. Give your answer to one decimal place and show your working.
