Answer:
(a) Magnitude: 14.4 N
(b) Away from the +6 µC charge
Step-by-step explanation:
As the test charge has the same sign, the force that the other charges exert on it will be a repulsive force. The magnitude of each of the forces will be:

K is the Coulomb constant equal to 9*10^9 N*m^2/C^2, q and qtest is the charge of the particles, and r is the distance between the particles.
Let's say that a force that goes toward the +6 µC charge is positive, then:


The magnitude will be:
, away from the +6 µC charge