问题
解答题
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答案
(1)3x+9=21
3x+9-9=21-9
3x÷3=12÷3
x=4;
(2)2x-3.9=8.5
2x-3.9+3.9=8.5+3.9
2x÷2=12.4÷2
x=6.2;
(3)16+8x=70
16+8x-16=70-16
8x÷8=54÷8
x=6.75;
(4)4x-6×7=78
4x-42+42=78+42
4x÷4=120÷4
x=30;
(5)5x+3=14.28
5x+3-3=14.28-3
5x÷5=11.28÷5
x=2.256;
(6)3x-16=71
3x-16+16=71+16
3x÷3=87÷3
x=29.