Dear David,

    I'm very glad you are arriving in my city at 3:00 p.m. this Sunday. Now let me tell you the way to the Blue Sky Restaurant. I'll meet you there. Take a taxi from the bus station and go down New Bridge Avenue. Go across the big bridge. When you see a bank, turn right and go through Bank Street. You'll pass three one-way avenues: Sixth Avenue, Seventh Avenue and Eighth Avenue. When you see a big McDonald's, turn left. Then go along Green Avenue until（直到）you see New Park. Turn left and go down Center Street. The Blue Sky Restaurant is on your right.

    I hope you have a good trip.

Yours,

Larry

宜宾是国家级历史文化名城，大观楼是标志性建筑之一（如图①）．喜爱数学实践活动的小伟查资料得知：大观楼始建于明代（一说是唐代韦皋所建），后毁于兵火，乾隆乙酉年（1765年）重建，它是我国目前现存最高大、最古老的楼阁之一．小伟决定用自己所学习的知识测量大观楼的高度．如图②，他利用测角仪站在B处测得大观楼最高点P的仰角为45°，又前进了12米到达A处，在A处测得P的仰角为60°．请你帮助小伟算算大观楼的高度．（测角仪高度忽略不计， $\sqrt{3}$ ≈1.7，结果保留整数）．

线段有限长，直线无限长．