Answer:
put 0 in y<=2x+4
y<=4
so if y=4, then y<=2x+4 is true, but y can not equal 4 because they don't want y<2x+4 be true. So y should be 3, 2, 1, 0.
(0, 2)
put -2 in y<=2x+4
y<=0
so if y=0, then y<=2x+4 is true, but y can not equal 0 because they don't want y<2x+4 be true. So y should be negative.
(-2, -1)
