(**20 POINTS**)
1/3 of the students in a school are in sixth grade.
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1. How many sixth graders are there if the school has 70 students?
2. How many sixth graders are there if the school has 28 students?
3. If the school has x students, write an expression for the number of sixth graders in terms of x.
4. How many students are in the school if 63 of them are sixth graders?
