To calculate the net electric force on each of the charges this is what you do:

For Part A: The force acting on charge 1 is as follows,

F1 = F21 + F31, (in other words the force acting on charge 1 is equal the force of charge 2 on 1, plus the force of charge 3 on 1)

After establishing this you go on to use the Electric Force Equation, which is:

F=(ke * q1*q2)/ r^2

where ke=8.988*10^9 N*m^2/C^2

and r is the distance between the two charges.

Do not forget to first conver the units of the charge and distance to the proper SI units of Coulomb and meter.

The direction can be determined based on the diagram, if two charges are alike then the force would point towards the other force, and if the charge are not alike then the force would point towards itself.