3m-2n=8 (2)

Solution: (1) Multiply both sides by 2 to get 4m-2n= 10 (3).

(3)-(2) m=2

Substitute (1), n=- 1.

2、2x-y=-4 ( 1)

x+3y=33 (2)

(2) If both sides are multiplied by 2, 2x+6y=66 (3)

(3)-( 1)，7y=70，y= 10。

Substitute (2), x=3.

3、x/2-2y=9/2 ( 1)

x+y/2=-9 (2)

(1) If both sides are multiplied by 4, 2x-8y= 18 (3).

(2) If both sides are multiplied by 2, 2x+y=- 18 (4)

(4)-(3)，9y=-36，y=-4。

Substitution into (2) gives x=-7.

4、2/3m+6n=3

3/8m-2n=3