Boston University Initial Acceleration of Particle Problems

Two particles are fixed on an x axis. Particle 1 of charge 72.1 μC is located at x = -6.51 cm; particle 2 of charge Q is located at x = 7.13 cm. Particle 3 of charge magnitude 27.6 μC is released from rest on the y axis at y = 6.51 cm. What is the value of Q if the initial acceleration of particle 3 is in the positive direction of (a) the x axis and (b) the y axis?