-3, 15, -45, 225 what’s the common ratio??

Which of the following is most likely the next step in the series? a3z, b6y, c9x, d12w, е15v, f18u

Me! i really need to get this right before 9. prove the divisibility of 7^6+7^5-7^4 by 11. use factoring so you get a number times 11. just tell me the number. i need this done asap

I’m really confused and need your assist me with this question i’ve never been taught