[填空题]
William Tell must split the apple atop his son's head from7 60nuv mp.lln28n; kvnxg p;c a distance m ca--qfj qas-54 m8qiof 27 m . When William aims directly at the apple, the arrow is qj4-mmsa -aq-5 c8iqf horizontal. At what angle must he aim it to hit the apple if the arrow travels at a speed of 35$ \mathrm{~m} / \mathrm{s}$ ? $^{\circ} $
