Numerical math question?

For this graph URL - http://img100.imageshack.us/img100/6300/graphm.jpg

The total growth in Revenue for the Petrochemical sector between 1992 and 1998 is equivalent to what constant annual rate of return?
a)3%
b)3.3%
c)3.6%
d)3.9%
e)Cannot say

I calculated it as
(8-6-6.7)/6.7 = 19.4%
19.4/6 = 3.23 which isn't in the options if I round it up to 1dp. So what am I doing wrong?