Find the electric potential difference between two charged spherical surfaces with charge +q and –q, radius Ra and Rb, respectively

A solid core carrying excess charge, Q = 46.4 μC, is located at the center of concentric spherical shells. The two spheres are joined by a hollow plastic tube that starts at the radius of the small sphere, r = 17.5 cm, and ends at the radius of the large one, R = 38.5 cm. When a charge, q = 6.9 μC, is placed at the inner end of the tube and released from rest, it accelerates straight through the tube and out the other end as shown. - kog ( ² = − 1 / 2 ) kQq R (a) How much did the electric potential energy change as the particle moved from one end of the tube to the other? Write your answer symbolically, in terms of Q, q, r, R and constants (as needed), then calculate its numeric value. AUE= = 8.97 X R x J (b) How much electric potential energy will be left when the little charge is 73.5 cm from the core? UE = 7.48 J 9

can you please ans (k)  & ( l)?

Identical point charges (+50 µC) are placed at the corners of a square with sides of 2.0-m length. How much external energy is required to bring a fifth identical charge from infinity to the geometric center of the square?