the sollution set {x,y}of the systemof equations x-2y=0 and 3x+4y=20 is
I would use substitution.
from x-2y = 0 ---> x = 2y
sub that into the 2nd:
3(2y)+ 4y = 20
continue to find y, then replace in x = 2y
from x-2y = 0 ---> x = 2y
sub that into the 2nd:
3(2y)+ 4y = 20
continue to find y, then replace in x = 2y