Hey guys, (and girls), I'm new here and I was wondering if someone could get me started on this problem:

Find y so that (4y+1)+(y+4)+(10-y) form a geometric series.

So far, I know the following:

T1=4y+1

T2=y+4

T3=10-y

Tn=ar^(n-1)

Thx in advance!

EDIT: I also know that I need to find 2 anwsers for r.