Accoring to the Chargaff's first rule of base pairing, each of the four nucleotide bases has its own complimentary match, that it always bids with.
So, Adenine always bonds with Thymine and Cytosine always binds with Guanine.
If you know the concentration of one base, in our case Cytosine, then you can easily calculate the percentage of other bases.
Since Cytosine and Thymine are always paired, there is an equal amount of both of them -16%.
So, 16% C + 16G = 32% of the whole DNA.
This means that the other two base pairs A and T make up to 68% of the DNA.
Half of the 68% is Adenine = 34% and half of it is Thymine- 34%.
So, the percentages of base pairs in the DNA sequence are :
16% C
16% G
34 % A
34 % T