The two horizontal lines are parallel, and there is a third line that intersects them as shown below.

If we know that the blue angle is `MEASURE` degrees, what is the measure of the orange angle?

`MEASURE`

init({
range: [ [ -1, 11 ], [-1, 4] ]
});
graph.pl = new ParallelLines( 0, 0, 10, 0, 3 );
graph.pl.draw();
graph.pl.drawTransverse( ANCHOR );
graph.pl.drawAngle( KNOWN_INDEX, true );
graph.pl.drawAngle( UNKNOWN_INDEX, false, "#FFA500" );

Opposite angles are equal, so the pink angle measures `MEASURE` degrees.

graph.pl.drawVerticalAngle( KNOWN_INDEX, true, "#FF00AF" );

The pink and orange angles are corresponding angles, so they are also equal.

The orange angle measures `MEASURE` degrees.

graph.pl.drawAngle( UNKNOWN_INDEX, true, "#FFA500" );

Note that the green angle also measures `MEASURE` degrees. This makes sense because it is opposite the orange angle and corresponds with the blue angle.

graph.pl.drawVerticalAngle( UNKNOWN_INDEX, true, "#28AE7B" );