Explanation:
as the intersection angles of parallel lines with a third line are the same for both parallel lines (and then vice versa for the other pair of parallel lines), we have a lot of equal angles here.
not to forget : the sum of all angles around a single point on one side of a line is always 180°.
51 = (y + z)
(6z + 9y) = x
x + (x + z) = x + 51 = 180°
x = 129°
we have now
y + z = 51
9y + 6z = 129
so,
z = 51 - y
9y + 6(51 - y) = 129
9y + 306 - 6y = 129
3y = -177
y = -59
z = 51 - y = 51 - -59 = 51 + 59 = 110
the value of z that makes j and k parallel is 110.