I need help with Part A and B

Two particles with equal charge + Q are sitting on the Y axis as shown in the figure. Another particle with the same charge (sign and magnitude) is fired from far away with initial velocity of vo on the X axis, towards the charges. A) what is the minimum initial velocity necessary for the particle to reach the origin? B) If the initial velocity is half of the velocity you found in A, at what distance to the charges on the Y axis does the charge stop moving due to the repulsive force