On leaving the University of Oxford, in 1676, Edmond Halley visited Saint Helena and set up an astronomical observatory with a 7.3-metre-long (24 ft) aerial telescope with the intention of studying stars from the Southern Hemisphere. The site of this telescope is near Saint Mathew's Church in Hutt's Gate, in the Longwood district. The 680-metre (2,230 ft) high hill there is named for him and is called Halley's Mount.

Answer this question, if possible (if impossible, reply "unanswerable"): How many feet was the telescope that was set up in the observatory?
24