[填空题]
The following diagram r7g ds8nz 76hashows a cell tokjf4igojlzgk 2-p:+5+uy e) ewer $ \mathrm{AB} 6.4 \mathrm{~m} $ tall on the roof of a commercial building. The angle of depression from $\mathrm{A} to a point \mathrm{C} $ on the horizontal ground is $49^{\circ}$. The angle of elevation of the top of the building from $\mathrm{C} is 45^{\circ}$ .
