Hi Farhaini, do you have the complete question or complete paper? I couldn’t find the paper from the internet 
it would be very helpful if you could share it! Thank you very much 
Question
Jika tempoh bumi mengelilingi matahari adalah satu tahun dan tempoh Planet
O adalah 12 tahun, cari jarak Planet O ke Matahari. Berikan jawapan dalam
sebutan r_o.
If the orbit period of the Earth around the Sun is one year and that of Planet O
is 12 years, find the distance of the Planet O to the Sun. Give the answer in
terms of r_o.
Answer
Hi Farhaini,
The question is flawed as they did not specifically mention what is r_o, and if r_o is the distance between Planet O and the sun then the answer would just be r_o 
The better question would be “Give the answer in terms of r_E, where r_E is the distance of the Earth to the Sun.”
I do agree with your working because you used the given information, but be careful as it is cube root and not square root, and you can just invert the fractions to get r_E and r_o as the numerator so you won’t make mathematical errors 
Hope this helps! You need not worry too much about this question because it’s not a properly phrased question to begin with