Help with simple question pls-screenshot_4.png

How did the guy calculate his rejection region next to the C's? Can someone show me the steps ?

MY steps for C=13 was P(Y>13 l P=1/2)
<=> 1- P(Y <13 l P=1/2)
<=> 1- P(Y < 12 l P=1/2)

My teacher told me that the answer was

But I do not know how 1- P(Y < 12 l P=1/2) can equal to 1-0.868=0.132 pls can someone help ?