A(n)=ar^(n-1) so
100=4r^9
25=r^9
ln25=9lnr
ln25/9=lnr
r=e^(ln25/9)
a(n)=4e^((n-1)(ln25/9) if you wanted an approximation...
a(n)=4(1.43^(n-1))
I don't know what posts are but i'm assuming you would subtract 21 from 17 and get 4.
Answer:
I think it might be 56 degrees
By using y=mx+b you get y=-3/8x-17/8
I'd say the 3rd one. I haven't done this stuff in 2 years ... me forgot. But if it's not right, then the 1st one!
I want you to know you're smart and you can do this! Good luck!