I get the prime factorization of 105,...

The problem

I get the prime factorization of 105, How did you get (i + 2) from 210

Since

105 = 3*5*7

and

210 = 2*105* = 2*3*5*7

we have

105i + 210 = 105*i + 2*105*

we pull "105*i" in front of brackets and get:

105*i + 2*105* = 105(i + 2) = 3*5*7(i + 2)