Answer:
30%
Explanation:
Considering that the amount of Cytosine added to the amount of Guanine is 40%, that explains that Cytosine and Guanine each equal to 20%.
Now, the remaining bit is 60%. Since Adenine and Thymine both equal the same, that would mean: 60/2 = 30.
Cytosine and Guanine pair together and will always be equal to one another. The same goes for Adenine and Thymine. (A=T, C=G)
Always remember that you want it to total up to 100% at the end.