Ive gotten to (60+x)/(100+x) = (100+x)(100+x).
Cross multiply to get 9600+x^2+200x = 10000 +200x + x^2.
Then 400 = 20x
The sequence is 80, 120, 180.
Then to find the common ratio, 120 divided by 80 is 3/2, and 180 divided by 3/2 is 120.
But it isn't right, and I can't find my mistake. Any help?