Dividend Growth Rate

The following question is form BPP Mock 1 MCQ question.
RZS Co has recently paid a dividend of 34c per share. 4 years ago the dividend was 12c a share. There was a 1:1 bonus issue of shares 2 years ago. Current share price is $5 a share.
What is the cost of equity capital for RZS Co?
A) 38.5%
B) 16.4%
C) 17.9%
D) 6.8%

This following is their explanation.
The bonus issue would have halved dividend per share, so the comparable dividend from 4 years ago is 12c x 2 = a share to ascertain growth.
Average growth rate is = (34/24)^1/4 – 1 = 9%

I think the growth rate should be g= (68/12)^1/4 – 1 (or) (34/6)^1/4 -1 = 54% because if there was no bonus issue, current dividend per share would be 34c x 2.
Please help me, Sir