Query about Question 6 from "PrepSwift: # of Numbers in Factorials III" [12707] 2

GRE GRE Quant Problem Solving
1

https://www.gregmat.com/quizzes/quiz/prepswift-of-numbers-in-factorials-iii (Question 6)

Feels so complicated. Kindly explain in a very simple way

2

Refer to Query about Question 6 from "PrepSwift: # of Numbers in Factorials III" [12707] Help - #4 by Kweku