x=1 and y=-1
Explanation:
Lets name the equations as
3y+7x=4 or 7x+3y-4=0.......................eq(1)
-6x+y=-7 or -6x+y+7=0......................eq(2)
multiplying eq(2) with 3 and subtracting eq(1) from eq(2)
(-6x+y+7=0)*3
(-18x+3y+21)-(7x+3y-4) =0
we can write it as
-18x+3y+21-7x-3y+4=0
-25x + 25=0
-25x=-25
x=1
plugging the value of x in eq(1)
7*1+3y-4=0
7+3y-4=0
3y+3=0
3y=-3
y=-1
so x=1 and y=-1