题目

The Earth is faced with a serious power problem now and all of us are affected by it. Should we leave everything to the government, or can we do something to save power? The answer is clear if not us, who? Let us look at how you can save power at home.Computer. More often than not, we do not turn off our monitors (显示屏) even after we have shut down our computers. And we often leave our computers on when we walk away to do something else. Keep the monitor and the computer switched off when you are not using them. Start doing this even when at work. You will help save some of the earth's im把一张边长为40cm的正方形硬纸板，进行适当地裁剪，折成一个长方体盒子（纸板的厚度忽略不计）．如图，若在正方形硬纸板的四角各剪掉一个同样大小的正方形，将剩余部分折成一个无盖的长方体盒子．要使折成的长方体盒子底面周长为120cm．那么剪掉的正方形的边长为多少？