Question

how to find factor of 8400

Answer 1

prime factorization?

Answer 2

8400 = 2 * 4200 = 2 * 2 * 2100 = 2 * 2 * 2 * 1050 = 2 * 2 * 2 * 2 * 525 =
2 * 2 * 2 * 2 * 5 * 105 = .....?....

Answer 3

You could use a prime factor calculator
http://1728.org/prime.htm
and your answer will be
2*2*2*2*3*5*5*7

Answer 4

and here's what Wikipedia says about finding prime factors:
http://en.wikipedia.org/wiki/Prime_factor