2、 13 + 2a

3、 1、5x 0.5x

4、a - 4

5、 17

6、m？ 2 m-5a

7、a - b a - b + c

8. (5.3+4.7)+a 2.4a+2.4? 2

9、3x - 5 4x - 5

10、5x

Second, 1,? 2、? 3、? 4、?

Third, 1, A 2, C 3, C 4, B 5, C 6, a.

Four. x = 10 x = 30.6 x = 45 y = 2.5

Verb (abbreviation for verb) negligence

Sixth, ellipsis

7. 1. Solution: Suppose there are X trees in the fourth grade. 2x - 40 = 120

2. Solution: Suppose that the first artificial earth satellite launched by the United States weighs X kilograms.

2x + 0.38 = 173 x = 86.3 1

3. solution: it takes x days for mercury to go around the sun.

4x + 13 = 365 x = 88

4. Solution: Let the unit price of white chalk be X yuan.

120x + 48 = 144 x = 0.8

5. Solution: We assume that water is X yuan per ton.

420x - 380x = 60 x = 1.5

March: 1.5? 420 = 630 (yuan)

April: 1.5? 380 = 570 (yuan)

6. solution: let the speed of train b be x kilometers.

(2x - 8)？ 4 = 480 x = 64

A: 64-8 = 56 (km/h)

Intelligent gas station

Four spellings. Is 42 cm the most paper-saving? wrapping paper