In sea urchin DNA, which is double-stranded, 17 % of the bases were...

In the DNA molecule, the nucleotides are base paired according to the Chargaff's rule of base equivalence, and it tells always tells adenine pairs with thymine and guanine pairs with cytosine.

$A = T, G = C$

C = $17$So G = $17$

$A + G / T + C = 1$

$A + G + C + T = 100$

A + $17 + 17$+ T = $100$

A + T = $100 - 34$

So, $A = 33$