An electron with a speed of 791 x 108 cms in the positive

Question

Compute each part of following question given below:

Question: An electron with a speed of 7.91 x 10⁸ cm/s in the positive direction of an x axis enters an electric field of magnitude 1.84 x 10³ N/C, traveling along a field line in the direction that retards its motion.

Part A: How far will the electron travel in the field before stopping momentarily?

Part B: How much time will have elapsed?

Part C: If the region containing the electric field is 8.38 mm long (too short for the electron to stop within it), what fraction of the electrons initial kinetic energy will be lost in that region?

I know the correct answer but explain how to get this answer!