1.x/3+y/4=3/4 ①
4（x+2）=3(y-4) ②
由②得x=3y/4-3 ③
将③代入①得y=7/2
将y=7/2代入③得x=-3/8
2.(x+y)/2+(x-y)/2=7 ①
4(x+y)-5(x-y)=2 ②
由①得x+y+x-y=14
x=7
将x=7代入②得y=1
3.(s-1)/5=(t+3)/2 ①
s-1/2=(1-t)/2 ②
由②得s=2-t ③
将③代入①得t=-13/7
将t=-13/7代入②得s=27/7
4.(2x-7y-8)二次方+|3x-8y-10|=0
由题意得2x-7y-8=0 ①
3x-8y-10=0 ②
由①得x=（8+7y）/2 ③
将③代入②得y=-4/5
将y=-4/5代入③得x=1/10