I'm going to tell you how to find the answer yourself so you can figure out other problems like it.
First, DNA is made up of those four nucleic acids. Adenine always pairs with Thymine in DNA. Guanine always pairs with Cytocine.
Therefore, the amount of Adenine will always equal the amount of Thymine in DNA. The amount of Guanine will always equal the amount of Cytocine.
So, if Adenine equals 23% of your sample and Adenine equals Thymine, then Thymine equals 23%.
Add the amounts of Adenine and Thymine. 23% + 23% = 46%
100% - 46% =
That gives you the percentage of Cytocine and Guanine together. Since they are in equal amounts, divide by two and you have the percentage of each.