A group of physical geography students measured the soil infiltration capacity at 11 different sample sites across a local drainage basin. Their measurements, in millimetres per hour (mm/hour\text{mm/hour}mm/hour), are recorded in the table below.
| Sample Site | Soil Infiltration Capacity (mm/hour\text{mm/hour}mm/hour) |
|---|---|
| Oak Ridge | 35 |
| Valley Bottom | 18 |
| Pine Forest | 74 |
| Bracken Slope | 50 |
| Riverside Path | 12 |
| Heather Moor | 65 |
| Willow Wetland | 24 |
| Gorse Heath | 58 |
| Sheep Pasture | 42 |
| Birch Copse | 85 |
| Clay Field | 31 |
Calculate the upper quartile value of this dataset. You must show your working out.