1练习十五第1题答案
12x = 90 × 0.8
12x = 72
x = 6
x - 9 = 10 ÷ 2.5
x - 9 = 4
x = 13
6.1x = 12.2
x = 2
2练习十五第2题答案
都不对，左边x = 4，右边x = 2.5
3练习十五第3题答案
（1）70 - x = 24
（2）420 = 6v
4练习十五第4题答案
3x = 58 - 22
x = 12
7x - 14 = 2x
5x = 14
x = 2.8
