(1)
7
8 x=
21
40
7
8 x÷
7
8 =
21
40 ÷
7
8
x=
3
5
(2)
1
3 x÷
4
5 =8
1
3 x÷
4
5 ×
4
5 =8×
4
5
1
3 x=
32
5
1
3 x÷
1
3 =
32
5 ÷
1
3
x=
96
5
(3)x+20×
1
4 =19
x+5=19
x+5-5=19-5
x=14
(4)x+
7
8 X=42
(1+
7
8 )X=42
15
8 X=42
15
8 X÷
15
8 =42÷
15
8
X=
112
5
(1)
7
8 x=
21
40
7
8 x÷
7
8 =
21
40 ÷
7
8
x=
3
5
(2)
1
3 x÷
4
5 =8
1
3 x÷
4
5 ×
4
5 =8×
4
5
1
3 x=
32
5
1
3 x÷
1
3 =
32
5 ÷
1
3
x=
96
5
(3)x+20×
1
4 =19
x+5=19
x+5-5=19-5
x=14
(4)x+
7
8 X=42
(1+
7
8 )X=42
15
8 X=42
15
8 X÷
15
8 =42÷
15
8
X=
112
5