My friend has a big police dog named Kim. Police dogs are often very smart. Every Sunday afternoon my friend takes Kim for a long walk in the park. Kim likes walking very much.
       One Sunday afternoon a man visited my friend. He talked to my friend for a long time. They talked and talked. Soon it was time for my friend to take Kim for his walk, but the man still stayed. Kim became very worried about his walk in the park. He walked around the living-room sometimes and at last sat down in front of the man and looked at him. But the man went on talking.
      After thirty minutes, Kim couldn’t stand(忍受) it. He went out of the room and came back a few minutes later.   He sat down in front of the man again but this time he held the man’s hat in his mouth.

如图是一个上下底密封纸盒的三视图，请你根据图中数据，计算这个密封纸盒的表面积为____ cm²．（结果可保留根号）．

送水员将两桶相同的纯净水送上位于五楼的小明家，可以有两种方法：一是将两桶水一起送上楼；二是分两次，每次送一桶水上楼，假设送水员的速度相同，前后两种送水方法的功率和机械效率分别为P₁、P₂和η₁、η₂，则下列选项正确的是（　　）

下列算式中，计算结果为x²－3x－28的是（    ）