Problem Solving

As shown in the figure above, from runway 1, airplanes must turn either 120degree to the right onto runway 2 or 135 degree to the left onto runway 3. Which of the following does NOT indicate a complete turn from one runway to another?

a) 30degree
b) 55degree
c) 60degree
d) 75degree
e) 105degree

OA is B, I liked the question, at first i was overwhelmed by the complexity and got it wrong...but found it pretty simple when i attacked it with a cool head..this is what happens on the 36th question

The above is from Peterson master the GMAT 2010 test 2