①

3

10

x-21×

2

3

=4

3

10

x-14=4　

3

10

x-14+14=4+14

3

10

x÷

3

10

=18÷

3

10

x=60．

②1

1

5

x+

2

5

x=

4

15

8

5

x=

4

15

8

5

x÷

8

5

=

4

15

÷

8

5

x=

1

6

．

③

0.25

x

=

1.25

3

1.25x=0.25×3

1.25x÷1.25=0.75÷1.25

x=0.6．

④x×（

3

4

-

2

3

）=

2

3

x×

1

12

=

2

3

x×

1

12

÷

1

12

=

2

3

÷

1

12

x=8．