A semicircle of radius a is in the first and second quadrants, with the center of curvature at the origin. Positive charge +Q is distributed around the left half of the semicircle (0 to 90 degrees) and negative charge -Q is distributed uniformly around the right half of the semicircle (90 to 180 degrees). Part A: what is the magnitude of the net electric field at the origin produced by this distribution of charge?

Express your answer in terms of variables Q, a, and appropriate constants.

Part B: what is the direction of the net electric field at the origin produced by the distribution of this charge?

+X direction, -X direction, +Y direction, or -Y direction