An investigator measured the rate of photosynthesis in a suspension of the green alga Chlamydomonas at different light intensities. They used a photosynthesometer to measure the distance moved by an air bubble in a capillary tube over a period of 25 minutes25\text{ minutes}25 minutes at each light intensity.
The table below shows the results of this investigation:
| Light intensity (klx\text{klx}klx) | Distance moved by bubble in 25 minutes25\text{ minutes}25 minutes (mm\text{mm}mm) | Rate of bubble movement (mm hour−1\text{mm}\,\text{hour}^{-1}mmhour−1) |
|---|---|---|
| 2.0 | 4.5 | 10.8 |
| 4.0 | 9.0 | 21.6 |
| 6.0 | 12.5 | RRR |
| 8.0 | 15.0 | 36.0 |
| 10.0 | 15.5 | 37.2 |
Calculate the value of R R\,R in the table. Show your working.