How do I simplify 12(2x-5)^5(1+5x)^3 + 15(2x-5)^6(1+5x)^2

Answer 1

well, I see a bunch of common (2x-5) and (1+5x) factors. So, I get
3(2x-5)^5 (1+5x)^2 (4(1+5x) + 5(2x-5))
= 3(2x-5)^5 (1+5x)^2 (30x-21)
= 9(2x-5)^5 (1+5x)^2 (10x-7)