zy+xy=180 (angles on a line =180)

120(zy) + xy=180

xy=60

now the other line's angles are xy, wx and kw which will all equal 180

you know that xy=60, wx=55, kw=?

which all add up to = 180 (angles on a line =180)

60+55+kw=180

180-115=kw

65=kw

check*

55(wx) +65(kw) = 120(zy)(vertically opposite angles are =)

120=120

Hope that helped?