A 0.165kg cue ball with an inital speed of 2 m/s bounces off the rail in a game of pool. For x and y axses located the counce reverses the y component of the ball's velocity but does not alter the x component(the angle is 30 in the negative x axis and it bounces across the y axis into an unknown angle).

Question

A 0.165kg cue ball with an inital speed of 2 m/s bounces off the rail in a game of pool. For x and y axses located the counce reverses the y component of the ball's velocity but does not alter the x component(the angle is 30 in the negative x axis and it bounces across the y axis into an unknown angle). 
a) what is the theda ? 
b) What is the change in the ball's linear momentum in unit vector notation?

what are the equations I would use? I don't understand what to do . I tries find theda by arctan(v_x/v_y) but I don't know what v_x and v_y are... Please help me.