solve the system 3x+4y=40 y-2y=0

Answer 1

3x+4y=40
y-2y=0

is that a typo in y-2y = 0 ???

I will assume you meant x-2y = 0, if so then
from the second, x = 2y

sub that back into the first and find y

I am sure you can take it from there.