An electron is held 360cm from an vertically aligned

Question

Solve the all parts of following problem:

Problem: An electron is held 3.60cm from an vertically aligned infinite charged plane and then released from rest. It accelerates toward the plane to the left and collides with a speed of 1.20×10⁷ m/s.

Part A: What is the surface charge density of the infinite plane?

Part B: What is the magnitude of the electric field at 7.20cm from the plane?

I need help to find the surface charge density of the infinite plane.