Hope someone help with this probability

This is a probability question in some language otherwise than English, I try to translate the meaning into English, and hope someone help.

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If there is a horizontal circular track, where two marbles moving on the track freely and randomly as they are released by the player. The two marbles will finally stop at two places of the track and they will create an angle to the center of the circular track, if the angle created is smaller than or equal to degree 30 , then the player will win $3, what is the probabilty of he winning $3

as well as the expected value, what is the expected value of this game?