\[tg\ 54{^\circ} = \frac{120}{l}\]
\[l = \frac{120}{tg\ 54{^\circ}} = 120\ ctg\ 54{^\circ} =\]
\[= 120\ tg\ 36{^\circ} \approx 120 \bullet 0,7265 \approx\]
\[\approx 87,18 \approx 87,2\ (м).\]
\[Ответ:\ \ 120\ tg\ 36{^\circ} \approx 87,2\ м.\]