Use the PRE tag! Your diagram is then this:
/ /
/ /
/ /
3x-33/ /
_____/___/________
/ / 2x+6
/ /
L M
Imagine the two parallel lines L and M collapsing to become one single line:
/
/
3x-33/
_____/________
/ 2x+6
/
L M
Vertical Angles Are Congruent.
Click on the hyperlink, "Show Source". See how the tags are made.