A study of Alpine deglaciation recorded the annual retreat of 15 major Swiss glaciers. The data collected (in meters) for a single hydrological year are shown in the table below.
| Glacier | Annual Retreat (m) |
|---|---|
| Aletsch | 115 |
| Gorner | 92 |
| Fiescher | 84 |
| Unteraar | 61 |
| Morteratsch | 76 |
| Rhone | 48 |
| Otemma | 103 |
| Findelen | 68 |
| Corbassière | 55 |
| Gauli | 42 |
| Zinal | 89 |
| Gries | 31 |
| Tschierva | 73 |
| Allalin | 50 |
| Roseg | 80 |
Calculate the lower quartile value of the annual retreat for these glaciers. You must show your working out.