you multiplique 7(-x+2y)=-21(7) to eliminated the x so : -7x+14y=-147 / 7x+3y=-6 = 0x+17y=-153 , so u divide by itself the 17y/17=-153/17 , so u get (y=-9) and u plug in the equation to find x ,: 7x+3(-9)=-6 , 7x-27=-6, 7x=-6+27 , and u get 7x=21, so u divide by itself 7x/7=21/7 , so you get (x=3)