Ok look at this problem as
25x^3+5x^2 and
-15x-3
with 25x^3+5x^2
they both are divisible by 5 (25/5 & 5/5) and since x^2 is the highest x they both have you can factor that too.
so 25x^3+5x^2
becomes
5x^2(5x+1) since you can take 5x^2 out of the original.
To do -15x-3
find what both can be factored by
both can be factored by -3 (-15/-3 & -3/-3)
since -3 doesn’t have an x we cannot favor and x out so.
-3(5x+1) would be the completed factor!
Please note when factoring a negative the signs will change and you can always make sure the answers right by FOILING