Question

I need to know if I am doing this problem right when sustitution method.
y+2x=3
y+2x=-4
y+2x=3 -1(y+2x=3)-y-2x=-4
now add the two equation
y-2x=3
-y-2x-4
the answer would be -4y=7
then divided -4=7 answer 1.75
I no that there is more to this answer I am just stuck and not sure if this is right are not.