There is an arrangement of three charges. There is one with 5.0 μC at the origin of some axis of coordinates. The second charge of -4.0 μC, is located in the coordinate (20 cm,30 cm) and the third charge, of 3.0 μC, is located at the point (25 cm,-50 cm). calculate:

a. electric potential at (30 cm, 0)
b. electric field at (30 cm,0)
c. the potential energy of the arrangement
d. the work needed to bring one particle of 1.5 μC from the infinite to the point (30 cm, 0)

Can anyone tutor me on answering this type of question?

Question

There is an arrangement of three charges.  There is one with  5.0 μC at the origin of some axis of coordinates. The second charge of  -4.0 μC, is located in the coordinate (20 cm,30 cm) and the third charge, of 3.0 μC, is located at the point   (25 cm,-50 cm). calculate:

a.	electric potential at (30 cm, 0)
b.	electric field at (30 cm,0)
c.	the potential energy of the arrangement 
d.	the work needed to bring one particle of  1.5 μC from the infinite to the point   (30 cm, 0)
 
Can anyone tutor me on answering this type of question?