If lines $j$ and $k$ are parallel, what is the value of $x$ in the figure shown?[asy]
label("$j$",(0,10),W);
draw((0,10)--(15,10),Arrow);
draw((15,10)--(0,10),Arrow);

label("$k$",(0,0),W);
draw((0,0)--(15,0),Arrow);
draw((15,0)--(0,0),Arrow);

draw((4,10)--(10,7));
draw((10,7)--(12,3));
draw((12,3)--(7,0));
label("$20^\circ$",(8,10),S);
label("$140^\circ$",(10,7),SW);
label("$x^\circ$",(12,3),W);
label("$30^\circ$",(10,0),N);
[/asy]