y1=-3/4x+1(1) y2=7/8x-5(2) y1+y2=-3(3)
由3得y1=-3-y2(4)
把(2)代入(1)得:-3-y2=-3/4x+1(5)
把(1)代入(5)得:-3-(7/8x-5)=-3/4x+1(5)
解得X=8