$8, Class 3 (1) 21 students made a total of 69 paper airplanes. Each girl made 2, and each boy made 5. So, there are ( ) boys and ( ) girls.

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【Analysis】Assuming all are girls, they can make 42 paper airplanes in total, which is 27 less than the actual 69 paper airplanes. For every girl replaced by a boy, 3 more paper airplanes can be made, so there are $27 \div 3=9$ boys, and 12 girls.