Solve each of the following systems of eqautions by the method of cross-multiplication:
2x-y=6
x-y=2
x=4,y=2
2x+y=35
3x+4y=65
2x+3y=13
5x−4y=−2
x+yxy=2,
x−yxy=6
x+ay=b
ax−by=c
5x+y−2x−y=−1
15x+y+7x−y=10