3. School cleaning, three years have eight students sweeping the floor, cleaning the table is twice as much, cleaning the glass than cleaning the table less than 3. How many students clean the glass?<br>4. Primary school students participate in greening activities. Three trees were planted by students in three years, and the number of trees planted in five years was four times of that in three years. How many more trees are there in five-year class than in three-year class?<br>
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